Late Quaternary paleoclimatic and paleoceanographic change over northern Chatham Rise, New Zealand

Marine Geology, 108 (1992): 383-404

383

Elsevier Science Publishers B.V., Amsterdam

Late Quaternary paleoclimatic and paleoceanographic change over northern Chatham Rise, New Zealand Juliane Fenner a, Lionel Carter b and Robert Stewart c aBundesanstalt fiir Geowissenschaften und Rohstoffe, Stilleweg 2, D-3000 Hannover 51, Germany bNew Zealand Oceanographic Institute, Private Bag, Kilbirnie, Wellington, New Zealand CDepartment of Soil Science, Massey University, Palmerston North, New Zealand (Received August 15, 1991; revision accepted May 6, 1992)

ABSTRACT Fenner, J., Carter, L. and Stewart, R., 1992. Late Quaternary paleoclimatic and paleoceanographic change over northern Chatham Rise, New Zealand. Mar. Geol., 108: 383-404. Four cores from the lower northwestern flank (3010-3726 m water depth) of the Chatham Rise, east of New Zealand, penetrated a post-glacial to last glacial sequence of mainly hemipelagic muds. An accurate time frame for this study is provided by well dated tephra layers and additional 14C-dates. A hiatus is detected at the core tops of all cores studied, with the last 900 to 1000 years missing. Sedimentological and micropaleontological analyses reveal that: (1) Isotope Stage 2 ended ca. 15000 yr B.P. After a transitional period with a fluctuating composition of planktonic foraminifera assemblages and fluctuating isotopic values more stable post-glacial conditions were established at ca. 10000 yr B.P. (2) From the end of Isotope Stage 2 to Isotope Stage 1 accumulation rates of diatoms, aeolian quartz and calcareous microfossils decreased stepwise by a factor of 10, 4, and ca. 1.5, respectively, in response to decreasing wind intensities and upwelling. (3) In spite of significant climatic and oceanographic changes from the last Glacial to the Present, the Chatham Rise has remained the northern distributional boundary for endemic subantarctic diatoms. This implies that east of New Zealand, the Subtropical Convergence has remained bound or close to the Chatham Rise during both glacial and post-glacial times. (4) Sediments are slight influences of contour currents or turbidity currents are recognised only in sediments younger than 16 000 years.

Introduction Sediments north and south of Chatham Rise

From Bounty Trough directly south of Chatham Rise a number of cores have been analysed for sediment deposition (Griggs et al., 1983; Nelson et al., 1985; Carter and Carter, 1988) illustrating a drastic change from hemipelagites with frequent turbidites in glacial periods, to calcareous biopelagites typical of interglacials. Whereas from north Correspondence to: J. Fenner, Bundesanstalt f/ir Geowissenschaften und Rohstoffe, Stilleweg 2, D-3000 Hannover 51, Germany. 0025-3227/92/$05.00

o f C h a t h a m Rise o n l y o n e core b e y o n d the shelf has b e e n s t u d i e d in detail, P 69 o n the w e s t e r n slope o f H i k u r a n g i T r o u g h in w h i c h t e r r i g e n o u s h e m i p e l a g i t e s a n d t u r b i d i t e s prevail in glacial as well as interglacial deposits, a l t h o u g h the l a t t e r have a h i g h e r b i o g e n i c c o m p o n e n t ( S t e w a r t a n d Neall, 1984).

Hydrography E a s t o f N e w Z e a l a n d , C h a t h a m Rise f o r m s a ca. 1300 k m long, e a s t - w e s t t r e n d i n g , s u b m a r i n e b a r r i e r (Figs. 1 a n d 2). T h e p r e s e n t d a y S u b t r o p i c a l C o n v e r g e n c e ( S T C ) is a l i g n e d a l o n g its typically

© 1992 - - Elsevier Science Publishers B.V. All rights reserved.

384

J. FENNER ET AL.

[] [ ]

]l [ ] II [ ] II [I [ ] [] []

~AUPO

Biogeniccalcareousooze Biogenicsand/grave~ Terrigenous mud Tenigenoussand/gravel Terrigereusmud/calc, ooze Deepocean clay

IT

BOUNTY TROUGH

C

175°E Fig. 1. Sedimentary and hydrographic regime east of New Zealand. Black arrows= surface water currents after Heath (1985), white arrows= bottom water current. Surface sediments after Mitchell et al. (1989). W.B.C. =western Boundary Current. Stars indicate the position of the cores.

200-400 m deep rise crest (Fig.l). This oceanic front is a zone of strong horizontal temperature and salinity gradients associated with strong mesoscale eddies. It separates subtropical surface waters (> 15°C summer temperature, > 10° winter temperature, and 35.7-35.8%o salinity) to the north from mixed temperate-subantarctic surface waters (< 14.5°C summer temperature, salinity 34.5°/oo or slightly higher) to the south (Garner, 1959; Heath 1981a,b). South of Chatham Rise, Antarctic Intermediate Water (AAIW) is identified by a salinity minimum of 34.3-34.4%o at water depths of 600800 m. Most of the AAIW probably flows northward around the eastern tip of Chatham Rise and gradually submerges below subtropical surface water. North of Chatham Rise AAIW with the characteristic salinity minimum is found at water

depths of 800-1200 m (Heath, 1981a,b). Periodically small amounts of AAIW also enter the Hikurangi Trough region by way of upweUing through Mernoo Saddle at the western end of the rise (Heath, 1972, 1981a,b). Pacific Deep Water (PDW) occurs below the AAIW and is identified on the northern Chatham Rise slope at depths below approximately 3000 m (Gilmour, 1973). It is characterised by a salinity maximum of 34.74%0. PDW is entrained - - together with underlying Antarctic Bottom Water (AABW) - - within a deep Western Boundary Current (Warren, 1973), that flows in northwest direction along the slope.

This project Five sediment cores were taken from the lower slope of northern Chatham Rise (Table 1; Figs.2

385

PALEOCLIMATIC AND PALEOCEANOGRAPHIC CHANGE OVER CHATHAM RISE

ND

40os -

COOK STRAIT

c.A?.A

u

A/SE

BOUNTY Fig. 2. Submarine topography (isobaths in meters) and location of cores. Line marks profile given in Fig.4: below 3000 m = echo sounder profile measured during R.V. Tangaroacruise 1146, above 3000 m = relief taken from N.Z. Oceanographic Institute Chart I : 1000000, Oceanic Series, Bathymetry, Bounty Sheet. 1963. TABLE 1 Location, water depth and length of the cores studied Core

Q858 Q859 Q860 Q861

Geographic Latitude

Longitude

39°49.6'S 39°56.4'S 40°16.3'S 40°14.5'S

178°03.5'W 178°29.8'W 179°03.9'w 179°24.1'W

Waterdepth (m)

Core length (m)

3735 3654 3216 3010

1.90 1.27

1.32 1.25

(only studied down to hiaxtus at 0.93m core depth)

a n d 4) d u r i n g New Z e a l a n d O c e a n o g r a p h i c Institute cruise 1146 with R.V. Tangaroa (Carter, 1980). The aim was to evaluate within a late Q u a t e r n a r y stratigraphic f r a m e w o r k changes ( 1 ) i n wind inten-

sity, as reflected by the a m o u n t s of aeolian quartz; (2) in p a l e o p r o d u c t i v i t y a l o n g n o r t h e r n C h a t h a m Rise, as d o c u m e n t e d by a c c u m u l a t i o n rates a n d a b u n d a n c e changes of different microfossil groups,

386

and to obtain (3) information on long-term shifts in the position of the Subtropical Convergence during the past ca. 20 000 years. The lowest of the five cores recovered, Q 857, in 4815 m water depth, lies clearly within the depth range influenced by modified AABW moving as a western boundary current along the base of Chatham Rise. This core has been reported on by Carter and Mitchell (1987). The four cores higher up on the slope (Q 858-Q 861), between 3010 and 3726 m water depth, are bathed by PDW entrained within the WBC, although outside the fast flowing sector of this current (Warren, 1973). This area just east of Hikurangi Trough is characterised by a high terrigenous component (McDougall, 1975; Mitchell et al., 1989). However it lies outside the main transport routes feeding the abyssal plains (Hikurangi Trough and Channell, Lewis, 1990; Fig.2). Accordingly, a relatively undisturbed and uninterrupted record from the last Glacial to the Present could be expected.

Methodology Prior to sampling, the split cores (maximum thickness 37 mm) were subjected to X-radiography t o identify sedimentary and bioturbatory structures. A Phillips "Macrotank" 140BE X-ray unit was used at settings of 90 kV and 2 mA. The cores were routinely sampled at 5 or 10 cm intervals, as well as below and above major lithologic and microfossil boundaries, and within tephra layers. Grain-size distributions were determined by pipette and sieve analysis, calciumcarbohate contents by acid titrimetry (Van der Linden, 1968), and the abundance of quartz by a quantitative X-ray diffraction method adapted from Johnson and Beavers (1959). The abundance of the following biogenic components >200 ~tm was determined: planktonic and benthic foraminifera, ostracodes, echinoid spines, crustacean fragments, radiolaria and siliceous sponge spicules. Further, the species composition of the planktonic foraminiferal assemblage was analysed. All quantitative data obtained are based upon a minimum count of 300 specimens at a magnification of x40. In order to be able to compare the results with those of Kennett (1968)

J. F E N N E R ET AL.

the > 125 ~tm fraction of Q 858 was analysed for abundance and left/right coiling ratio of Neoglo-

boquadrina pachyderma. In addition, the abundance of diatoms per gram sediment and the species composition of the planktonic diatom assemblage were determined quantitatively. For this purpose a dried, weighed aliquot of bulk sediment was boiled in an equal mixture of 10% HC1, and 30% H20 / to dissolve the calcium carbonate, and oxidise organic carbon. Clay was removed using a differential settling technique outlined by Fenner (1982, 1985). Quantitative slides with a statistically homogeneous particle distribution were prepared following the method of Batterbee (1973). The mounting medium was hyrax (refractive index n.d.=l.71; solvent toluene). The diatom species were identified, and counted using a Leitz Orthoplan photomicroscope with an oil immersion objective (PL APO Oel 100/1.32), and a working magnification of 1000 x. Radiocarbon age determinations, using accelerator mass spectrometry (Inst. of Nuclear Sciences, D.S.I.R., Wellington), were performed on planktonic foraminifera from three depth intervals in Q 858. Oxygen isotopes were measured on selected species of benthic foraminifera, Uvigerina hispida, U. peregrina, Cibidoides wuellerstorfi, and C. kullenbergi. Detailed results on isotope studies of cores Q 860, and Q 858 will be published in a paper in preparation. Accumulation rates (A) were calculated for the intervals in between well dated ashes, and radiocar-

Gt

bon dated samples using A = S V~n"M (S= sedimentation rate, M =abundance of component in the bulk sediment). The dry bulk density

~n

was determined by measuring the weight of a known volume of freshly cored sediment after it had been dried to 105°C.

Results

Stratigraphy A stratigraphic framework for the cores was derived from (1) radiocarbon dates on planktonic

387

PALEOCLIMATIC AND PALEOCEANOGRAPHIC CHANGE OVER CHATHAM RISE

foraminifera from core Q 858, (2) tephrachronology and (3) oxygen isotope curves derived from benthic foraminifera.

Radiocarbon dates and tephrachronology Radiocarbon ages in core Q 858 were obtained near points where the planktonic foraminifera assemblages change (Fig.3): 60- 65 cm 10 860_+ 170 yrs B.P. NZ 603A 110-115 cm 16 110_+210 yrs B.P. NZ 604A 160-165 cm 18650_+380 yrs B.P. NZ 605A Five tephra layers were identified (Figs.3 and 5; Table 2). Two of these, the Waimihia Ash, and the Rerewhakaaitu Ash, can be recognised macroscopically. The remainder were found during microscopical analysis of the sediments. Using their mafic mineral assemblage, stratigraphic position, and, in the case of the Waimihia Ash, glass shard chemistry (analyses performed by P.C. Frogatt, Victoria University, Wellington), these ashes were correlated with radiocarbon dated, rhyolitic tephra on North Island, New Zealand (Vucetich and Pullar, 1964, 1969; Healy et al., 1964), and with marine tephra on the continental slope off eastern North Island (Lewis and Kohn, 1973). The youngest tephra identified is the Kaharoa Ash, dated as 930_+70 yr B.P. (NZ 10A). It is documented as an ash-rich layer of coarse grain size (fine to medium sand) in the tops of cores Q 859, Q 860 and Q 861. In Core Q 858 this ash is missing due to a hiatus. All cores contain a 1.5 2cm thick, rhyolitic tephra at around 10-20 cm depth. The tephra has a high abundance of particles > 200 ~tm, and contains only traces of heavy minerals (dominantly hypersthene and augite). These minerals and the glass shard chemistry (Kohn and Glasby, 1978; P.C. Frogatt, pers. commun., 1988), are consistent with that of the Waimihia Ash, which originated from Taupo region, and is dated as 3440_+70 yr B.P. (NZ 2A). Below the Waimihia Ash is an interval with fluctuating but generally high amounts of glass shards in the sand fraction. In two of the cores, Q 860 and Q 861, peaks in the abundance curves of sand-sized vesicular ash suggest the presence of at least two ash layers, in this stratigraphic position (Fig.5). These, however, remain unidentified.

A fine-grained (coarse silt to fine sand) ash-rich layer, present in all cores, is regarded as the Waiohau Ash (11250+200 yr B.P. NZ 568 A) on the basis of a radiocarbon dated level (10 860 _+ 170 yr B.P.) just 5-10 cm above the ash in Q 858. Cores Q 858 and Q 859 further contain a fine sand-sized tephra with a conspicuous biotite component (> 50% of the ferromagnesian assemblage) together with hypersthene, hornblende, and (rare) augite. This mafic mineral assemblage, and the tephra's stratigraphic position near a change from glacial to interglacial conditions (cf. Stewart and Neall, 1984) indicate it is the Rerewhakaaitu Ash dated as 14700_+200 yr B.P. (NZ 716A). In the only core reaching into the last Glacial, Q 858, another abundance peak of vesicular ash in the sand fraction was found at 165 cm core depth, just below a radiocarbon dated level of 18650_+380 yr B.P. This age suggests the ash probably is the Okareka tephra (estimated age from terrestrial sequences ,-~ 19000 yr B.P.). The wide spread and prominent Kawakawa tephra (22590-+290 yr B.P., Wilson et al., 1988), which should be macroscopically visible, was not recovered in Q 858. The base of this core therefore probably is younger.

Oxygen isotope stratigraphy The oxygen isotope curves from benthic foraminifera fit the time framework supplied by the tephra and radiocarbon dates. Just below the Rerewhakaaitu Ash, in Oxygen Isotope Stage 2, occur the last characteristic glacial 6180-values around 5%o. And fully postglacial conditions in oxygen isotope Stage 1, with 6180-values between 3.8 and 3..1%o are established above the Waiohau Ash. The interval in between with rapid changes in oxygen isotope values is called Termination I (Broecker and Van Donk, 1970), and generally shows in three steps: Terminations IA, IB, Ic (Duplessy et al., 1981; Mix and Ruddiman, 1985). Of these, Terminations IA and I B and possibly also Ic can be identified in Q 858. In cores Q 858 and Q 859 the base of Termination IA is between 14 500 and 15 500 years old, which agrees with the time range determined by Bard et al. (1987a,b), for northern hemisphere core (H-73-139 (Rockall Plateau) from shells of Globigerinoides bulloides,

388

J. FENNER ET AL

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PALEOCLIMATICAND PALEOCEANOGRAPHICCHANGEOVER CHATHAM RISE

389

TABLE 2 Core depths (in centimeters) of ashes recognised in the cores on the northern slope of Chatham Rise Ash

Years B.P.

Q 861

Kaharoa Ash Waihmihia Ash Waiohau Ash Rerewhakaaitu Ash

930 + 70 3440+70 11250 ___200 14700 + 200

0-1 17-18 90 -

and with results by Broecker et al. (1988). These authors give ages between 14500 and 15000 yr B.P. for the base of Termination I. For the end of Termination IB the same authors give ages between 9400 and 9900 yr B.P. In cores Q 858 and Q 859 the end of a termination lies at an age of approximately 10000-10 500 yr B.P. As changes in oxygen isotopes and sedimentological/micropaleontological parameters occur close to tephra of known age, these deposits were chosen as isochrons to correlate the cores, and are used to separate stratigraphic units of different paleoclimatic and paleoceanographic conditions (Table 3). Unit I roughly represents the post-glacial period. Unit II is the transitional period, in which the strong changes from the last Glacial to the Post-glacial occur in all parameters investigated. Unit III roughly encompasses the final phase of

Q 860 0-1 21-22 130 -

Q 859

Q 858

0-1 14.5-16.0 72 100

l 1.5-13.0 65 97

the last Glacial. Unit IV is differentiated from Unit III by slight changes in the assemblage composition of planktonic foraminifera and diatoms. The cores thus provide largely complete sediment sections representing the past 20000 years. Sediment is missing only at the surface in all cores. In cores Q 859, 860 and 861 the Kaharoa Ash is right at the sediment surface, indicating nondeposition or erosion for the last ca. 930 years. In Q 858, further down on the slope, this hiatus spans an even longer time interval as the Kaharoa Ash is missing.

Sedimen tology Sediment composition The four cores studied reveal a threefold downcore colour zonation (Fig.4). At their tops (down

TABLE 3 Sedimentation rates (cm/1000 years) calculated for Units Ib to IV Unit

Definition

Ib

Kaharoa Ash to Waimihia Ash

Ia

II

III

III

Waimihia Ash to Waiohau Ash

Years B.P.

Q 861

Q 860

Q 859

Q 858

930 + 70 7.0

8.0

5.8

<4.4

9.2

13.8

8.3

6.6

7.8

8.7

3440 + 70 3440 __+70 11250 __+200

Waiohau Ash to Rerewhakaaitu Ash

11250 + 200

Rerewhakaaitu Ash to 14C-dated level

14700 + 200

14C-dated level to 14C-dated level

16110 + 210

14700 + 200

11.3 16110+210

19.7 18650 ___380

390

J. F E N N E R

O--

0.861

0.860

Q859

0.858

(3010 m)

{32A1 m)

(3654m

3726m) Wm

. . . .

Turbidite ?

Contourite ?

~ Bioturbation

I

o.

~

Macrotephra layer

I

S

Hemipelagite Mud

Ash- rich layer.

5 0,5

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ET AL.

Wispy Laminae

rrrrrrm~

Re

1.0i

, I

Re

COLOUR 1,5-

yellow brown 10YR 512 green grey

5G 6/1

olive grey

5Y 6/1 olive grey 5Y 512

2.0 0 1000 - -

CHATHAM

2000 NE

T~ 3000 A000 5000

CHATHAM RISE - N o r t h

Flonk

Fig. 4. Down-slope-profile from the lower part of the northern slope of Chatham Rise (compare Fig. 2), showing the location of the cores, sedimentary structures, and sediment colors. Wm=Waimihia Ash, Re= Rerewhakaaitu Ash. WBC=core of Western Boundary Current.

to ca. 2-5 cm depth) all cores have yellow-brown coloured mud (10 yr 5/2). Below down to 75-90 cm core depth sediment colour is olive-grey (5y 6/1) or green-grey (5g 6/1), while below, the remainder of the cores is olive-grey (5y 5/2). Throughout, the sediments of cores Q 858Q 861 can be classified as strongly silty clays (nomenclature after Miiller, 1961; Folk, 1965) with minor amounts of sand (< 5%). The sand consists predominantly of foraminifera and radiolaria except for where volcanic ashes are present and the sand fraction may increase up to 15%. The terrigenous sand component is sparse.

In the coarse sand fraction (> 200 ~tm) there are just single sporadic quartz grains. And in the fine sand fraction (63-200 ~m) quartz is present consistently, but in low amounts. A special feature in post-glacial sediments are layers in which the fine sand-sized quartz is enriched far above the general background low abundance (Fig.4), and which accordingly are clearly recognisable on the X-radiographs (for more details see chapter "sediment facies"). The main silt-sized components are diatom valves, a biogenic, marine, planktonic component and quartz, a land-derived component. While the

PALEOCLIMATIC AND PALEOCEANOGRAPHIC CHANGE OVER CHATHAM RISE

overall quartz contents (which in the cores studied here is mainly silt-sized quartz) of post-glacial sediments (younger than approximately 10000 years) fluctuate between 20 and 40%. Consistently high values around 40% are characteristic for the transitional interval (Unit II), and the last Glacial (Units III and IV; older ca. 15000 yr B.P.; Fig.5). Diatom valves generally, (if silica dissolution has not destroyed the record) correlate in their abundance with primary productivity. Diatom abundance increases from 0.6-6 million diatom valves/ gram sediment in the Post-Glacial to 10-20 million in sediments older than ca. 15 000 yr B.P. (Fig. 8). No textural trends are evident with increasing water depth or distance from the rise crest, and a down core trend can only be recognised in Q 858, where the clay content in post-glacial sediments (Unit I) is on average 7% higher than in Units II-IV. The calcium carbonate content (Fig.5; Table A1) of the post-glacial Unit I fluctuates between 30 and 40%, but is lower in the tephra due to dilution. During the transitional Unit II (older than ca. 11 000 yr B.P.) the calcium carbonate content of the sediments decreases, and reaches a minimum 10-20% in glacial sediments (Unit III and IV).

Sediment facies Two basic sediment facies, hemipelagites and turbidites, were identified on the basis of grain size, coarse fraction composition, and sedimentary structures portrayed on X-radiographs (e.g. Stow and Piper, 1984). Hemipelagites form the dominant facies(Fig.4). Most of the clay-dominated muds belonging to this facies are structureless. But some intervals are bioturbated. Primary layering is also occasionally evident, and consists of faint bedding and zones of "wispy laminae", which Hill (1984) regards as part of the hemipelagic facies. The second type of sediment - - although not coarser than the sediment above and below - - is characterised by a high abundance of fine sandsized quartz. On X-ray radiographs these sediments display many of the characteristics of mud turbidites, namely sharp bases followed by an' upcore sequence of irregular silt laminae and homogeneous mud bioturbated at its top (see

391

Piper, 1978). Such sequences are not common, but were detected, in all cores from the lower part of Unit I to the upper part of Unit III (Fig.4). These layers are up to 100 mm in thickness. The cores Q 858 and Q 859, each contain two prominent horizons of this facies type, which can be correlated on the basis of sediment composition, grain size and stratigraphic position. Interestingly, these layers neither coincide with abundance peaks in sandsized, shallow water biogenic components such as benthic foraminifera (Fig.7), nor with silt-sized, allochthonous microfossils, like shallow water diatoms (Fig.8). Such components could be expected if these sediments were redeposited from shallow slopes bordering the Chatham Rise or Hikurangi Trough. These results still allow for three possible explanations: (1) the coarse biogenic particles may have settled out from the turbidity current prior to its passage onto the lower Chatham Rise slope; (2) these deposits result from turbidity currents mobilised in deep water environments similar to the extensively slumped continental slope off Hawke Bay (Lewis 1973) or (3) the layers could be a product of winnowing induced by intensified activity of the deep western boundary current. In addition, considering the high clay content of the sediments, and the proximity of Hikurangi Trough, it is possible that the cores also contain mud turbidites in the guise of 1-10 cm thick beds of unbioturbated mud. The fine fraction of turbidites could have escaped over the rims of the canyon and settled out outside the trough. Such mud turbidites would not be detectable with the methods applied.

Accumulation rates of the main sediment components Determination of accumulation rates for intervals between well-dated horizons (Table 3; Fig.6) illustrates: (1) an overall trend to lower accumulation rates at the sites lower at the slope, (2) a ca. 3 fold decrease in bulk sediment accumulation rates in core Q 858 from the last Glacial (ca. 15 000-21 000 yr B.P.) to the post-Glacial, and (3) higher accumulation rates for all major com-

392

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A bulk

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Fig. 6. Q 858. Accumulation rates of the bulk sediment and main sediment components: calcium carbonate, quartz and diatoms. Calculations of the accumulation rates were done assuming constant sedimentation rates between radiometricallydated samples. In addition average component accumulation for core intervals between radiometricages is shown. ponents during the last Glacial compared to postglacial sediments. Of these, diatom accumulation decreased by a factor of 4-10 and aeolian quartz accumulation by 2-4, while that of calcium carbonate decreased only by 1.5-2. Therefore, it is not decreased carbonate production and sedimentation which cause the lower carbonate content of glacial sediments (Fig.5), but rather increased dilution by a more enhanced supply of biogenic siliceous particles and terrigenous quartz. As the cores are well above the carbonate compensation depth of 4500 m (Berger and Winterer, 1974) calcium carbonate dissolution is not considered to be a major factor.

Micropaleontological results Planktonic foram&ifera Changes in the composition of planktonic foraminifera assemblages ( > 200 ~m) are known to be correlated to paleotemperatures of surface waters down to a few hundred meters depth, and to paleofertility. As such they are an useful tool in Quaternary ecostratigraphy. The species are subdivided into four groups (Fig.3):

(i)

tropical-subtropical-temperate planktonic foraminifera species; (ii) the dominant species Globorotalia inflata; (iii) cold-temperate species and (iv) subantarctic species, which are selected on the basis of their modern geographic distribution in the Southwestern Pacific (Kustanovich, 1963; B6, 1967, 1977; Berger, 1969; Parker and Berger, 1971; Eade, 1973). Among the subtropical species Globorotalia hirsuta, G. truneatulinoides, G. crassula are relatively common, and Orbulina universa, and Globigerinoides ruber (white) rare. Globigerina ealida, Globi-

gerinella aequilateralis, Globigerinita glutinata, G. bradyi, Sphaeroidinella dehiscens and Globorotalia seitula occur only sporadically. Whereas these subtropical species are encountered in glacial as well as post-glacial sediments, other tropical-subtropical species like Globerigerinoides trilobus sae-

culifer, G. conglobatus, G. adamsi, Candeina nitida, Pullenia obliquiloculata, Hastigerinella digitata and Globigerina rubescens are completely absent in glacial sediments and very rare in post-glacial deposits. The abundance of the dominant species, the

394

temperate Globorotalia inflata, increases from approximately 50% in last glacial sediments to 80-85% in near surface sediments. Among the cold-temperate species group Globigerina bulloides is most abundant. It is plotted together with Neogloboquadrina dutertrei and Globigerina falconensis. The latter is included in this group because taxonomic assignment to either G. bulloides or G. falconensis was not clear in all specimens. The cold-temperate to subantarctic species group is dominated by Neogloboquadrina pachyderma. Very rarely, specimens of Globigerina quinqueloba also occur. In agreement with oxygen isotope stratigraphy, more cooler water indicating species in the assemblages of planktonic foraminifera are more abundant only at the base of core Q 859 and in the lower part of Q 858 (Unit III). In core Q 858 this interval, characterised by a maximum in subantarctic planktonic foraminifera species and a minimum in subtropical species, ends about 5 cm below the Rerewhakaaitu Ash. Contrary to the strongly fluctuating assemblage composition of Unit II, the planktonic foraminifera assemblage composition in Unit III remained constant for approximately 4500 years. Only below, in Unit IV, the assemblage composition changes to slightly higher values of subtropical and lower ones of subantarctic planktonic foraminifera species. In the transitional Unit II, above the Rerewhakaaitu Ash, the temperate-subantarctic species decrease in abundance, while subtropical species increase, as does G. inflata. The major post-glacial increase in abundance of subtropical species occurs at the base of this unit. In the upper part of Unit II the gradual assemblage change is interrupted by a relatively shortlived abundance peak of subantarctic and temperate-subantarctic species and a decrease in subtropical species. In the same interval oxygen isotopes shift to heavier values (compare Fig.3). Just above this cold interval G. inflata shows its strongest increase in abundance and a reduction of cold-temperate species takes place. This level coincides roughly with the stratigraphic position:of the Waiohau Ash (ll 250 yr B.P.). The post-glacial sediments can be subdivided at a level where Neogloboquadrina pachyderma becomes very scarce Coincident with an increase

~. F E N N E R ET AL.

in abundance of tropical-subtropical and subtropical-temperate planktonic foraminifera species. This assemblage change occurs at roughly 6000 yr B.P. Another change occurs at approximately 4000 yr B.P. where N. pachyderma and cold temperate species further decrease while G. inflata reaches maximum values. This second faunal change occurs near a pronounced and well-dated ash layer, the Waimihia Ash (3440 yr B.P.), which therefore is used to separate Subunit Ia from Ib.

Benthic foraminifera and other calcareous shelled benthos The main biogenic components in the sand fraction, besides planktonic foraminifera and radiolaria are benthic foraminifera (Fig.7). Accessory components are spines of irregular echinoides, ostracod shells, siliceous sponge spicules, and rare chitinous fragments of crustaceans. Benthic foraminifera in glacial and post-glacial sediments reflect intact, autochthonous slope assemblages without admixtures from the shelf. They are dominated by infauna. The epifauna making up < 15%. This benthos composition suggests a nutritious substrate and thus a high input of organic carbon. Also the species composition is typical of assemblages in high productivity areas. Distinct changes in the benthic foraminifera assemblages were noted from glacial to post-glacial sediments. Glacial assemblages are rich in Pyrgo and in fragile, infaunal species of the genera Chilostomella, Dentalina and Oolina. Post-glacial assemblages are more diverse, and almost lack, fragile infaunal species. Besides Uvigerina spp., the following are also present, Melonis balearis, Globobulimina spp., Sphaeroidina bulloides and Fissurella spp., and firmly cemented arenaceous foraminifera, e.g. Egerella parkerae, Sigmoilopsis schlumbergeri, Kareriella novanglae, K. bradyi and Martinotiella communis. The faunal change from glacial to postglacial sediments may reflect de facto assemblage changes related to changes in food supply. A second faunal change towards a higher abundance of agglutinated foraminifera (in Unit Ib and upper Ia) occurs in the upper part of all cores. Here limonitic fragments of the epifaunal Saccorhiza ramosa are particularly common and Rhab-

395

P A L E O C L I M A T I C A N D P A L E O C E A N O G R A P H I C C H A N G E O V E R C H A T H A M RISE

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396

damm&a, Trochammina, Cribrostomoides, Cystammina, Cyclammina and Rheophax also occur. This near-surface abundance peak of arenaceous foraminifera may be a preservational phenomenon. It is likely that shells of these species were originally present further downcore but their weakly cemented shells disintegrated, and cannot be recognised. With ostracoda, changes in diversity of the assemblages and in species abundance are similar to those in benthic foraminifera (Fig.7). Ostracods are scarce in glacial sediments and are nearly exclusively species of the genus Krithe. By comparison, post-glacial diversity is much higher, and in addition to Krithe also species of the genera Henryhowella, Poseidonamicus and Cytheropteron (N. Mostafawi, pers. commun., 1990) are present. The assemblages are considered authochthonous and typical for the deep sea.

Siliceous microfossils As in planktonic foraminifera, the planktonic diatom assemblages in post-glacial sediments have common tropical-subtropical species, but they are dominated by temperate to cold-temperate species. This is in spite of the location of cores Q 858 861 north of the Subtropical Convergence and below subtropical surface water (Figs. 1, 3 and 8). Subantarctic planktonic diatom species, which at present are common south of Chatham Rise (J. Fenner, 1988, unpubl, data), occur only sporadically at the core sites on its northern slope. The abundance fluctuations of selected diatom species and species groups are plotted in Fig.8. As an example of subtropical species Nitzschia marina shows minimum abundance (< 2%) during glacial times (older than 15 000 years), increases in transitional Unit II to values around 5% and reaches highest abundances (10 15%) in sediments representing the past ca. 6000 years. Endemic subantarctic-antarctic species comprise Fragilariopsis kerguelensis, Thalassiosira lentiginosa, and single finds of Fragilariopsis curta, Schimperiella antarctica and Thalassiosira gracilis. The downcore abundance plot of this group does not show the reverse trend to that of warm water species. Rather, endemic subantarctic-antarctic diatoms are extremely rare in glacial sediments.

J. F E N N E R ET AL.

But they occur with increased relative abundances (up to 4% of the diatom assemblage) during late post-glacial times (younger than ca. 6000 years). An earlier isolated abundance peak occurs in core Q 858 about 14000 15000 yr B.P. During the late post-glacial when their abundance increased, there is a similar increase of allochthonous coastal diatoms. This correlation suggests that subantarctic diatoms probably are also not part of the plankton communities flourishing over the northern slope of Chatham Rise but that they are allochthonous. Spores of the genus Chaetoceros, an indicator of high primary productivity, are abundant in sediments older than ca. 10000 years, and dominant in glacial sediments older than 15 000 years where they make up 70-80% of the diatom assemblage. As high abundance of Chaetoceros resting spores is paralleled by a high abundance in total diatom abundances and diatom accumulation rates, the abundance curve of the relatively dissolution resistant Chaetoceros resting spores can be interpreted as reflecting primary productivity over the northern slope of the Chatham Rise rather than dissolution effects. Radiolaria, like diatoms, are enriched relative to calcareous microfossils in glacial sediments older than 15 000 years (Fig.7). This enrichment is probably not caused by dissolution of foraminifera because in this case the plankton/benthos ratios of foraminifera should be low. Rather the rate of production and accumulation of radiolarians must have been increased during glacial times relative to that of planktonic foraminifera. The situation is different for post-glacial sediments. Here radiolarians increase in abundance towards the core tops. As this increase occurs together with the increase in benthic foraminifera and in fragmented planktonic foraminifera this relative enrichment in radiolarians seems to be due to calcium-carbonate dissolution.

Interpretation and discussion of results

Depositional processes Except for the missing core tops the cores provide a near-complete and undisturbed documenta-

397

P A L E O C L I M A T I C A N D P A L E O C E A N O G R A P H I C C H A N G E OVER C H A T H A M RISE

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398

tion of predominently hemipelagic deposition on northern Chatham Rise. Although the cores are marginal to the Hikurangi Trough with its active channel (Lewis and Kohn, 1973; Lewis, 1990) the sedimentological results reveal little turbidity current activity in the study transect. The biogenic silt and sand fractions consist nearly exclusively of autochthonous pelagic components and of autochthonous benthic slope organisms. The rare allochthonous components such as the silt-sized freshwater diatoms and coastal diatoms were not restricted to coarser layers but occur rarely throughout the cores. So, they are unlikely to have settled out from turbidity currents. Thus, if the studied sites are affected by turbidity currents it is mud turbidites. For this the high clay content of the sediments might provide an argument. Fine suspensates carried by turbidity currents coming down Hikurangi Trough may have swept over the edges and settled out on the slope. Layers with evident sorting effects like enrichment of terrigenous silt may reflect periods of winnowing on the slope at 3000-3800 m by WBC. At this depth range such winnowing effects are most evident in sediments with an age of ca. 9000 to 11 000 years.

Watermass characteristics and climate change Life conditions in surface waters over northern Chatham Rise have gradually changed since the last Glacial (Unit III) which is indicated by a series of shifts in the diatom and foraminiferal assemblages. These changes coincide with shifts in oxygen isotopes in shells of the deep-water reflecting Uvigerina spp., and therefore seem to be related to paleoceanographic and paleoclimatic changes. With the existing sample spacing of one sample per every 500 to 1500 years no leads or lags in deep water (3700 m) oxygen isotope changes versus surface water mass changes documented in the planktonic foraminifera assemblages could be detected. As the overall shift in 6180 values in benthic foraminifera shells from the last Glacial to the post-Glacial is only slightly larger than 1.2-1.6%o (ice-effect) PDW temperature remained fairly constant during glacial and post-glacial times.

J. F E N N E R ET AL.

The most prominent paleoceanographic change occurred at the end of the last Glacial somewhere between 15500 and 14500 yr B.P., when the temperate, subtropical and tropical planktonic foraminifera species increased, while temperatesubantarctic, and subantarctic species, as well as resting spores of the diatom genus Chaetoceros decreased. This trend is indicative of a reduction in nutrient levels and, in addition, reflects a slight contemporaneous warming of the surface waters. During the deglaciation phase (Unit II), from ca. 15000-11000 yr B.P., subtropical-tropical species became more frequent in the planktonic assemblages while species that indicate high productivity decreased. This general trend was interrupted near the end of Unit II by a period of cooler, more fertile surface waters. This interpretation is based on the change (a) in the composition of planktonic foraminiferal assemblages and (b) in oxygen isotopic composition of Uvigerina spp. (Fig.3) and (c) of Globigerina bulloides (Cuthbertson, 1989). This interval with higher productivity and possibly slightly cooler surface waters lasted approximately from ca. 14000 to 12000 yr B.P. South of Chatham Rise a similar interval with heavier oxygen isotopes during the transitional phase can be recognized in core Q 208 (Sarnthein et al., 1988). In fact such shifts in t~180 values during deglaciation, between Termination I A and IB, are found worldwide although at slightly younger ages and with shorter durations (e.g. Mangerud, 1980; Sarnthein et al., 1982; Duplessy et al., 1986; Bard et al., 1987; Broecker et al., 1988). This difference in age and duration may be caused by our assumption of constant sedimentation rates between the Waiohau and Rerewhakaaitu Ashes. At ca. 10000-10500 yr B.P. post-glacial conditions became established as is reflected in the plankton assemblages and oxygen isotopes. Within this post-Glacial (Unit I) signals for surface water and deep water changes differ. While oxygen isotopes of benthic foraminifera do not reflect distinct changes in deep water characteristics the surface watermasses reflecting planktonic foraminiferal assemblages do show contemporaneous shifts in all cores. E.g. a period with maximum abundances of subtropical-tropical species is indicated for ages from ca. 6000 to 4000 yr B.P. Another core interval

PALEOCLIMATIC AND PALEOCEANOGRAPHIC CHANGE OVER CHATHAM RISE

for which the assemblage composition of planktonic foraminifera changes to a species composition suggesting slightly warmer surface water temperatures whereas oxygen isotope values in benthic foraminifera do not reflect a time equivalent change in deep water characteristics is found in last glacial sediments, older than 18650 yr B.P. (Unit IV). The change to maximum values of the temperate and relatively dissolution-resistant species Globoratalia inflata though, which occurs in the uppermost part of all cores with tropical-subtropical as well as temperate-subantarctic species abundances remaining low or even decreasing is caused by selective dissolution of the more delicate shells at a time of markedly lower sedimentation rates and/ or possible winnowing. The increased fragmentation of planktonic foraminifera and the lower plankton/benthos ratio of foraminifera are used as an indication that calcium carbonate dissolution has especially effected the upper parts of the cores. Aeolian input - - wind intensity - - upwelling along northern Chatham Rise Silt-sized quartz in marine sediments often contains aeolian quartz that can be used as an indication of wind intensity (Rex et al., 1969; Scheidegger and Krissek, 1982). In the southwest Pacific, Thiede (1979) and Stewart and Neall (1984) reported increased silt-sized quartz accumulation for last glacial sediments east of Australia and New Zealand. They interpreted it as aeolian in origin and therefore as an indicator of increased wind intensity during glacial times. From these observations they concluded that during glacials the mid-latitude belt of strong westerly winds in the southwest Pacific shifted further north than at present. In addition, Stewart and Neall (1984) found peak rates of aeolian deposition towards the end of the last Glacial (ca. 15 000-17000 yr B.P.), which they interpret as evidence of sparsely vegetated aggradational surfaces in the lowlands. Such aggradational surfaces were in part built up by rivers in southern North Island (compare Cowie and Milne, 1973; Selby, 1976) and in part were formed by exposed continental shelf, particularly west of North Island, during lowered sea level (Fleming, 1962; Lewis and Eade, 1974). These

399

sparsely vegetated lowlands could have functioned as enlarged source areas for windblown particles. Our results from core Q 858 show maximum accumulation rates of quartz in sediments of the last Glacial between ca. 19000 and 16000 yr B.P. (Fig.6). Accumulation rates of windblown particles drop dramatically at ca. 16000-15000 yr B.P. At our sites, approximately 400 km distant from land, the reduction is three to fourfold compared to the > 10-fold reduction registered by Stewart and Neall (1984) only approximately 120 km distant from land. Further support for increased westerly wind intensities over the Chatham Rise during Glacials comes from the upwelling history along its northwestern flank. Even for the Present, with lower wind intensities, upwelling and associated increased primary productivity are inferred from surface sediments on the slope of northwestern Chatham Rise by the abundance of key diatom species (J. Fenner, 1988, unpubl, data). Indeed proof for more intensive upwelling during the last Glacial is provided by the accumulation rates of diatom valves being about one order of magnitude higher than during postglacial times and by the high abundance of productivity indicators such as Chaetoceros valves, bristles, and resting spores. Furthermore, the higher accumulation rates of calcareous microfossils and radiolaria support intensified glacial productivity and upwelling. The Subtropical Convergence ( STC) With the cooler surface water temperatures and the northward shift of the belt of westerlies during the last Glacial the question arises as to whether the STC, presently aligned along Chatham Rise, had shifted to the north in the last Glacial. In order to be able to trace the STC it is necessary to have parameters which can be used to define it. In this study we use the geographical distribution of plankton species, for which the STC forms the northern or southern limit of occurrence. Present knowledge on the geographic distribution of planktonic diatom species (see Guillard and Kilham, 1977) allows definition of several characteristic species for each: tropical, subtropical, temperate, subantarctic and antarctic surface waters. In these watermasses these species

400

have their abundance maximum, but their geographic occurrence is much wider. Only a few ecological studies identify the limiting factors and distributional limits of single species. Without such knowledge "unusual behaviour" of species abundances, such as the near absence of subantarcticantarctic diatom species in sediments of the last Glacial but their presence in post-glacial sediments, cannot be explained. In order to fill this information gap, a systematic study on the distribution and abundance of planktonic diatoms in surface sediments of the southwest Pacific, north and south of Chatham Rise (J. Fenner 1988, unpubl, data) was performed. Of those results the following is relevant to this study and the position of the STC. The geographic distribution of most tropical-subtropical and subtropical-temperate planktonic diatoms is not controlled by the position of the STC. Rather many of these species decrease in abundance well north of the convergence or are present in similar abundances on either side of it. This suggests that their distribution is controlled by nutrient availability rather than by temperature. In contrast, subantarctic species seem to be endemic to the subantarcticantarctic realm, (compare also Fenner, 1988). If nutrients are available, as they are in the surface waters east of New Zealand, for subantarctic species the strong temperature gradient associated with the STC becomes the limiting factor. East of New Zealand these species occur in large quantities (20-75% of the diatom assemblage) south of the STC, especially Fragilariopsis kerguelensis and Thalassiosira lentiginosa as well as less abundant T. gracilis, E curta and Schimperiella antarctica. However, they do not occur to the north of the STC inspite of nutrient-rich surface waters there. The sporadic valves of subantarctic species found in sediments on the north of Chatham Rise are interpreted as being displaced. Occasional transport across the Chatham Rise by eddies, or by currents around the rise, or through Mernoo gap may be possible causes. The scarcity of these species north of Chatham Rise suggests that once transported into subtropical surface waters these species probably do not multiply anymore. This abundance distribution of these subantarctic species in surface sediments makes them suitable

J. F E N N E R ET AL.

to use their down core occurrence and abundance patterns for tracing shifts of the STC during the Quaternary. The downcore distribution pattern of subantarctic species in each of the four cores on the northern Chatham Rise is very similar (Fig.8). Throughout post-glacial times the situation seems to have been like today with some specimens of endemic species being occasionally flushed across or around the rise. The near-absence of these species in glacial sediments north of the rise implies that even during the last glacial period the STC was either stationary or only shifted slightly to the north, but did not reach core sites Q 859 and Q 858. The low relative abundance of subantarctic diatoms in glacial sediments (Fig.8) can be explained by dilution as accumulation rates of planktonic diatoms at that time were approximately 1 order of magnitude (= 10 times) higher than post-glacial rates (Fig.6). Thus the most probable scenario for the last Glacial is a STC bound to Chatham Rise with subantarctic diatom species flourishing south of it like in post-glacial times and being transported north occasionally. The only difference being much higher accumulation rates of autochthonous diatoms diluting the concentration of these allochthonous components in the sediment. In the case of planktonic foraminifera, published data from surficial sediments (compare Kustanovich, 1963; Hayward, 1983) suggest that the present STC is not a distinct distributional boundary. According to their data, only the relative abundances of the species change at this oceanic front, e.g. the tropical-subtropical species Globigerinella aequilateralis, Globigerinafalconensis and Neogloboquadrina dutertrei decrease in abundance near the STC, and the subantarctic to antarctic species Globorotalia cavernula, which is rare south of Chatham Rise, is not found by them north of it. Kennett (1968) noted that dextral coiled shells of Neogloboquadrina pachyderma increase from 30 to 70% in surface sediments south of Chatham Rise to more than 90% north of it, with the overall abundance of N. pachyderma (> 125 ~tm fraction) decreasing from > 30% south of the STC to less than 20% north of it. This pattern is confirmed by the microfauna in the coretops on northern Chatham Rise. Here,

PALEOCLIMATIC AND PALEOCEANOGRAPHIC CHANGE OVER CHATHAM RISE

N. pachyderma ( > 1 2 5 g m fraction) makes up < 5% of the planktonic foraminifera assemblage with more than 90% dextral forms. In the glacial sections of our cores north of Chatham Rise the abundance of N. pachyderma is indeed higher (20-30%). But the percentage of dextrally coiled shells remains > 90%. This infers that even during the last Glacial, characteristic subantarctic faunas did not occur at the core sites. This contention is supported by an absence of the subantarctic G. cavernula, even in glacial sediments. Furthermore, the abundance of G. inflata, never falls below 5 20%, which is reported as characteristic for the >210gm fraction in surface sediments south of Chatham Rise (Griggs et al., 1983). According to these authors, rather the dominant species south of the Chatham Rise is G. bulloides (45-75%), whereas in our cores, even during glacial times, this species never exceeds 20%. The results from planktonic foraminifera are not as clear as those from planktonic diatoms. But the comparison of the present day geographical distribution of planktonic foraminiferal species with their downcore compositional changes also imply that although surface waters over the northern slopes of Chatham Rise were possibly cooler and upwelling increased during the last Glacial, but that the STC remained located over the Rise and did not reach sites Q 858 and Q 859. It is possible that in glacial times the rise crest became an even more effective trap for the convergence because of the glacio-eustatically lowered sea level. The observed stability of an oceanic front of course does not apply to regions with no such bathymetric constraint. Based on results of Hays et al. (1976) and Burckle (1984) from the Atlantic and Indian sector of the Southern Ocean, the Subantarctic Front appears to have shifted slightly northward and the late spring/early summer seaice cover may have shifted northward up to several degrees of latitude. As a consequence of the position of the STC remaining fixed to the Chatham Rise in glacial times, oceanic fronts in the region directly east and southeast of New Zealand must have moved closer together.

Conclusions Phytoplankton as well as planktonic and benthic foraminifera assemblages show that the northwest-

401

ern flank of Chatham Rise is presently overlain by subtropical surface waters and experiences moderate upwelling. During the last Glacial, accumulation rates of all biogenic components and also of terrestrial, windblown particles were much higher. This is assumed to be a response to an equatorward shift of the westwind belt, the availability of nonvegetated soft rock areas from which aeolian sediments were derived, and associated increased upwelling during the last Glacial. Parameters including: (1) oxygen isotopes of the benthic foraminifera Uvigerina spp., representing changes in Pacific Deep Water (PDW), (2) Chaetoceros spp. and total diatom abundance, documenting productivity, (3) quartz accumulation rates, documenting wind intensity (4) composition of diatom and foraminifera assemblages, documenting a slight increase in surface water temperature, all show their strongest change between 15 500 and 14 500 yr B.P. No paleoceanographic leads or lags could be recognized with the sample spacing available. A second interval of higher productivity and heavier oxygen isotopes in the PDW is recognised between 14000 and 12000 yr B.P. Post-glacial conditions with reduced productivity and lighter oxygen isotopes in the PDW were established at ca. 10000 yr B.P. In spite of such paleoceanographic and climatic changes, the Subtropical Convergence has remained bound to the Chatham Rise as indicated by the distribution and abundance of endemic subantarctic-antarctic planktonic diatom species (like e.g. Nitzschia kerguelensis and Thalassiosira lentiginosa) and planktonic foraminifera (like e.g. Neogloboquadrina pachyderma dextral).

Acknowledgements This study was generously supported by DFGscholarship Fe 240/1-1 to J. Fenner. We thank the Isotopenlabor der Universitiit Kiel, H. Erlenkeuser and I. Klein, for measuring oxygen isotopes. For these analyses benthic foraminifera of cores Q 859 and Q 861 were picked and cleaned by K. Winn, University of Kiel. The Uvigerina spp. picked by us for oxygen isotope determinations in cores Q 858 and Q 860 were cleaned by M. Hahn,

402

J. FENNER ET AL.

University of Kiel, who also provided technical and moral support. Helpful discussion with T. Barnes from "DSIR, Division of Information Technology, Lower Hurt, N.Z.", and H. Kassens, and E. Vogelsang at the "GPI, Univ. Kiel", are greatfully acknowledged.

J. Fenner thanks "NZOI" for its hospitality during several months in 1986 and 1987. The authors thank F. Jansen and E. Olausson for reviewing the manuscript and helpful comments.

Appendix Sedimentological parameters of the bulk sediment: weight percent (1) of calcium-carbonate and (2) of quartz; (3) bulk density (mass of dry sediment/volume of wet sediment) Core depth

Q 858

(cm)

1

0 5 l0 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 I10 115 120 125 130 135 140 145 150 155 160 165 170 175 180 185

23 26 27 22 33 30 37 29 37 30 38 35 30 28 29 35 25 17 23 24 26 15 20 24 24 12 21 16 19 13 21 8 18 14 17 13 18 19

Q 859 2

3

1

0.88

23 20 22 16 25 30 32 38 34 35 32 30 33 29 34 28 40 25 27 26 27 25 21 24 17

23 1.04 37 0.90 36 0.83 27 0.84 28 0.81 40 0.79 46 0.83 41 0.83 43 0.83 32 0.91 45 0.83 42 0.83 43 0.84 41 0.81 43 0.76 42 0.79 43

0.97 0.84

37

Q 860 2

3

I

0.88

29 25 28 18 25 29 32 28 33 27 28 29 33 30 30 30 31 30 29 31 32 30 38 27 36 26

28 1.04 10 0.93 37 0.83 38 0.79 33 0.79 22 0.81 30 0.79 39 0.74 33 0.72 39 0.76 34 0.81 41 0.76

Q 861 2

3

1

0.88

30 24 28 17 30 30 34 29 38 29 37 33 34 31 27 28 23 26 25 22 21 16 19 27

26 0.83 10 0.81 28 0.76 26 0.88 25 0.74 32 0.76 32 0.70 32 0.72 27 0.67 32 0.81 10 0.69 29 0.67 26

2

3 0.91

30 1.00 22 0.87 25 0.89 33 0.76 43 0.87 28 33 29

0.74 0.76

28 0.76 28 26 26

0.80 0.80

21 0.87 27

PALEOCLIMATIC AND PALEOCEANOGRAPHIC CHANGE OVER CHATHAM RISE

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