- Email: [email protected]
Oxygen isotope fractionation during the life and death of diatoms
506
Abstracts / Quaternary International 279-280 (2012) 462–565
understanding the mechanisms of human dispersal and anticipated nature of environmental conditions during that time. OXYGEN ISOTOPE FRACTIONATION DURING THE LIFE AND DEATH OF DIATOMS Jonathan Tyler. University of Oxford, United Kingdom E-mail address: [email protected]
Oxygen isotope analysis of diatom silica (d 18Odiatom) is rapidly becoming established as a palaeoclimate proxy using lake and marine sediments. In principle, the oxygen isotope ratio of diatom silica is a function of the isotopic composition of ambient water and growth temperature. However, exact controls over d18Odiatom remain poorly understood, including the fractionation associated with silica biomineralisation during diatom growth, and the effects of diagenetic processes operating post death. Early culture experiments and observations of isotope fractionation from field samples suggest an underlying temperature dependence on silica-water fractionation of w–0.2&/oC during diatom growth. However, significant d 18Odiatom offsets have been observed between living diatoms and surface sediments which suggest that diagenetic processes also affect the sedimentary signal. Here, we address these uncertainties using laboratory cultures of freshwater and marine diatoms. In particular, we assess the thermal dependency of fractionation between diatom species and the influence of additional ‘vital’ effects. In addition, isotope fractionation associated with experimental condensation of fresh diatom silica is investigated. New results will be presented and discussed with respect to establishing best practice for the laboratory treatment of diatom silica, and for interpreting past climate change from sedimentary d 18Odiatom records. ORBITAL AND MILLENNIAL SCALE MONSOONAL VARIABILITY OVER THE LAST GLACIAL-INTERGLACIAL CYCLE: THE ORGANIC CARBON RECORD FROM LAKE SUIGETSU, JAPAN Jonathan Tyler. University of Oxford, United Kingdom E-mail address: [email protected]
The accumulation rate of organic matter in lake sediments and its C/N and 13 12 C/ C ratios document changes in aquatic primary productivity and the transport of terrestrial organic matter over time. At Lake Suigetsu, Japan, increases in the accumulation of both authocthonous and allocthonous organic carbon are interpreted to be an indirect function of climate, whereby warm, wet conditions stimulate increased productivity in both aquatic and terrestrial ecosystems. During the last glacial-interglacial cycle (w140 ka – present) the carbon isotope composition of organic matter at Suigetsu co-varies with pollen- inferred precipitation, with both exhibiting marked w20ka periodicity typical for the precessionally driven East Asian Monsoon (EAM). The Suigetsu lake-catchment system also responded on shorter, millennial timescales, which is particularly evident in the organic carbon accumulation rate. Similar patterns of change between Lake Suigetsu and both the Greenland and Antarctic ice core records imply both intra- and inter-hemispheric climate teleconnections. These possible links will be discussed with respect to the driving forces behind the East Asian Monsoon, its impact on the Japanese climate and environment and the significance of these findings from a global perspective. SEDIMENTARY RECORD OF AN ICE/BED INTERFACE MOSAIC: DEFORMING SPOTS INTERVENING WITH STABLE BED AREAS AT SAMPłAWA, NORTHERN POLAND Karol Tylmann. Nicolaus Copernicus University, Poland E-mail address: [email protected]
Recent investigations suggest co-existence of stable and deforming patches transient in time and space at the ice/bed interface under large Pleistocene ice sheets, but unequivocal evidence of pervasive subglacial deformation is notoriously difficult to provide. Here, we present a sedimentary record of deforming spots and intervening non-deforming areas under the last Weichselian ice sheet in northern Poland based on a detailed study of the Samp1awa gravel pit exposure. The site is located within a morainic plateau in northwestern part of the Lubawa Upland. Exposed along a 70-m-long section is a Weichselian basal till up to 4 m
thick resting on undeformed outwash deposits up to 2 m thick. The till is typically massive sand-rich diamicton and its contact with the outwash sediments is mostly sharp and erosive. At the bottom of the till three, up to 15 m wide and up to 0.7 m thick bodies consisting of heavily deformed sediment, have been mapped. These bodies are characterized by upwardconvex shapes and consist of sandy-gravelly structureless deposits mixed to a different degree with till. Their basal contacts to undeformed throughcross bedded outwash deposits are erosive whereas their contacts to the overlying massive till are mainly transitional. Preliminary studies suggest that these bodies represent three subglacial deforming spots, whereby sorted sediments originally deposited in the ice/bed interface channels were subsequently deformed and mixed with debris released from the ice sole. Between these patches no evidence of subglacial deformation was found, supporting the model of selective subglacial deformation. THE NATURAL LENGTH OF THE CURRENT INTERGLACIAL Chronis Tzedakis. University College London / Department of Geography, United Kingdom E-mail address: [email protected]
Part of the scientific rationale for pursuing studies of past interglacials is that they provide potential analogues for the current interglacial. In this respect, intervals characterized by an orbital geometry similar to present may be particularly useful, because they can clarify our present position within the interglacial cycle and, by extension, indicate when the onset of the next glacial period should normally occur (or have occurred) in the absence of any anthropogenic interference. A key aspect in the search for orbital analogues is the subdued amplitude of precessional changes as a result of the modulating effect of the 400-kyr eccentricity cycle, which characterizes the current interglacial. This suggests that closer analogues should occur at times of lowest eccentricity values, representing multiples of w400-kyr intervals. Marine Isotope Stage (MIS) 11 (w400 ka) has traditionally been considered a potential analogue for the Holocene, but closer examination reveals distinct differences in terms of the phasing of precession and obliquity and deglaciation trajectories. This complicates the alignment of the two interglacials and underlines the limitations of the MIS 1 - MIS 11 analogy, suggesting that alternative candidates ought to be explored. Loutre & Berger (2000) found a slightly higher correlation of mid-June insolation between MIS 1 and 19 (w 785 ka) compared to that of MIS 1 and 11. While it is impossible to match precisely the phases of all three astronomical parameters from two different periods, the phasing between obliquity and precession in MIS 1 and MIS 19 is similar, which means that the alignment of the two intervals is not contentious. In theory, if the analogy with MIS 1 is correct, the duration of MIS 19 could be used to assess the natural length of the current interglacial. In practice, constraining the timing of glacial inception during MIS 19 is far from straightforward, but alternative lines of evidence might be explored. MULTIBEAM BATHYMETRIC AND SEDIMENT PROFILER EVIDENCES FOR ICE GROUNDING AND CRATER ON THE CHUKCHI AND BEAUFORT BORDERLAND, ARCTIC OCEAN Masao Uchida. National Institute for Environmental Studies, Japan E-mail address: [email protected]
Multibeam bathymetry and 12 kHZ-subbottom profiler data collected from the Japanese R/V Mirai in 2004 and 2008 provide convincing evidence for ice grounding scour and mega craters on the Chukchi and Beaufort borderland, Arctic Ocean. Previous studies (eg. Jakobsson et al., 2004) were reported in the same kind of large scour on the Chukchi Borderland. However, the bathymetric data is limited in the Arctic Ocean. In this study, we obtained bathymetric dataset of approximately 610000 km2 in area and running time of seabeam system was more than about 700 hours. Seabeam data were converted and visualized by CARIS (Geospatial Software Solutions) and ArcGIS (ESRI). We have described detailed pictures of this region for the first time. As a result, our data show a large number of craters and scour exist on the Chukchi and Beaufort borderland by the water depth of 3500m, suggesting that ice shelves including mega rock carried from unstable continental ice sheet was occupied with the Arctic Ocean during past deglaciation. This is the valuable information to consider the range and scale of the ice sheet collapse in the past deglaciation. However, formative
Abstracts / Quaternary International 279-280 (2012) 462–565
understanding the mechanisms of human dispersal and anticipated nature of environmental conditions during that time. OXYGEN ISOTOPE FRACTIONATION DURING THE LIFE AND DEATH OF DIATOMS Jonathan Tyler. University of Oxford, United Kingdom E-mail address: [email protected]
Oxygen isotope analysis of diatom silica (d 18Odiatom) is rapidly becoming established as a palaeoclimate proxy using lake and marine sediments. In principle, the oxygen isotope ratio of diatom silica is a function of the isotopic composition of ambient water and growth temperature. However, exact controls over d18Odiatom remain poorly understood, including the fractionation associated with silica biomineralisation during diatom growth, and the effects of diagenetic processes operating post death. Early culture experiments and observations of isotope fractionation from field samples suggest an underlying temperature dependence on silica-water fractionation of w–0.2&/oC during diatom growth. However, significant d 18Odiatom offsets have been observed between living diatoms and surface sediments which suggest that diagenetic processes also affect the sedimentary signal. Here, we address these uncertainties using laboratory cultures of freshwater and marine diatoms. In particular, we assess the thermal dependency of fractionation between diatom species and the influence of additional ‘vital’ effects. In addition, isotope fractionation associated with experimental condensation of fresh diatom silica is investigated. New results will be presented and discussed with respect to establishing best practice for the laboratory treatment of diatom silica, and for interpreting past climate change from sedimentary d 18Odiatom records. ORBITAL AND MILLENNIAL SCALE MONSOONAL VARIABILITY OVER THE LAST GLACIAL-INTERGLACIAL CYCLE: THE ORGANIC CARBON RECORD FROM LAKE SUIGETSU, JAPAN Jonathan Tyler. University of Oxford, United Kingdom E-mail address: [email protected]
The accumulation rate of organic matter in lake sediments and its C/N and 13 12 C/ C ratios document changes in aquatic primary productivity and the transport of terrestrial organic matter over time. At Lake Suigetsu, Japan, increases in the accumulation of both authocthonous and allocthonous organic carbon are interpreted to be an indirect function of climate, whereby warm, wet conditions stimulate increased productivity in both aquatic and terrestrial ecosystems. During the last glacial-interglacial cycle (w140 ka – present) the carbon isotope composition of organic matter at Suigetsu co-varies with pollen- inferred precipitation, with both exhibiting marked w20ka periodicity typical for the precessionally driven East Asian Monsoon (EAM). The Suigetsu lake-catchment system also responded on shorter, millennial timescales, which is particularly evident in the organic carbon accumulation rate. Similar patterns of change between Lake Suigetsu and both the Greenland and Antarctic ice core records imply both intra- and inter-hemispheric climate teleconnections. These possible links will be discussed with respect to the driving forces behind the East Asian Monsoon, its impact on the Japanese climate and environment and the significance of these findings from a global perspective. SEDIMENTARY RECORD OF AN ICE/BED INTERFACE MOSAIC: DEFORMING SPOTS INTERVENING WITH STABLE BED AREAS AT SAMPłAWA, NORTHERN POLAND Karol Tylmann. Nicolaus Copernicus University, Poland E-mail address: [email protected]
Recent investigations suggest co-existence of stable and deforming patches transient in time and space at the ice/bed interface under large Pleistocene ice sheets, but unequivocal evidence of pervasive subglacial deformation is notoriously difficult to provide. Here, we present a sedimentary record of deforming spots and intervening non-deforming areas under the last Weichselian ice sheet in northern Poland based on a detailed study of the Samp1awa gravel pit exposure. The site is located within a morainic plateau in northwestern part of the Lubawa Upland. Exposed along a 70-m-long section is a Weichselian basal till up to 4 m
thick resting on undeformed outwash deposits up to 2 m thick. The till is typically massive sand-rich diamicton and its contact with the outwash sediments is mostly sharp and erosive. At the bottom of the till three, up to 15 m wide and up to 0.7 m thick bodies consisting of heavily deformed sediment, have been mapped. These bodies are characterized by upwardconvex shapes and consist of sandy-gravelly structureless deposits mixed to a different degree with till. Their basal contacts to undeformed throughcross bedded outwash deposits are erosive whereas their contacts to the overlying massive till are mainly transitional. Preliminary studies suggest that these bodies represent three subglacial deforming spots, whereby sorted sediments originally deposited in the ice/bed interface channels were subsequently deformed and mixed with debris released from the ice sole. Between these patches no evidence of subglacial deformation was found, supporting the model of selective subglacial deformation. THE NATURAL LENGTH OF THE CURRENT INTERGLACIAL Chronis Tzedakis. University College London / Department of Geography, United Kingdom E-mail address: [email protected]
Part of the scientific rationale for pursuing studies of past interglacials is that they provide potential analogues for the current interglacial. In this respect, intervals characterized by an orbital geometry similar to present may be particularly useful, because they can clarify our present position within the interglacial cycle and, by extension, indicate when the onset of the next glacial period should normally occur (or have occurred) in the absence of any anthropogenic interference. A key aspect in the search for orbital analogues is the subdued amplitude of precessional changes as a result of the modulating effect of the 400-kyr eccentricity cycle, which characterizes the current interglacial. This suggests that closer analogues should occur at times of lowest eccentricity values, representing multiples of w400-kyr intervals. Marine Isotope Stage (MIS) 11 (w400 ka) has traditionally been considered a potential analogue for the Holocene, but closer examination reveals distinct differences in terms of the phasing of precession and obliquity and deglaciation trajectories. This complicates the alignment of the two interglacials and underlines the limitations of the MIS 1 - MIS 11 analogy, suggesting that alternative candidates ought to be explored. Loutre & Berger (2000) found a slightly higher correlation of mid-June insolation between MIS 1 and 19 (w 785 ka) compared to that of MIS 1 and 11. While it is impossible to match precisely the phases of all three astronomical parameters from two different periods, the phasing between obliquity and precession in MIS 1 and MIS 19 is similar, which means that the alignment of the two intervals is not contentious. In theory, if the analogy with MIS 1 is correct, the duration of MIS 19 could be used to assess the natural length of the current interglacial. In practice, constraining the timing of glacial inception during MIS 19 is far from straightforward, but alternative lines of evidence might be explored. MULTIBEAM BATHYMETRIC AND SEDIMENT PROFILER EVIDENCES FOR ICE GROUNDING AND CRATER ON THE CHUKCHI AND BEAUFORT BORDERLAND, ARCTIC OCEAN Masao Uchida. National Institute for Environmental Studies, Japan E-mail address: [email protected]
Multibeam bathymetry and 12 kHZ-subbottom profiler data collected from the Japanese R/V Mirai in 2004 and 2008 provide convincing evidence for ice grounding scour and mega craters on the Chukchi and Beaufort borderland, Arctic Ocean. Previous studies (eg. Jakobsson et al., 2004) were reported in the same kind of large scour on the Chukchi Borderland. However, the bathymetric data is limited in the Arctic Ocean. In this study, we obtained bathymetric dataset of approximately 610000 km2 in area and running time of seabeam system was more than about 700 hours. Seabeam data were converted and visualized by CARIS (Geospatial Software Solutions) and ArcGIS (ESRI). We have described detailed pictures of this region for the first time. As a result, our data show a large number of craters and scour exist on the Chukchi and Beaufort borderland by the water depth of 3500m, suggesting that ice shelves including mega rock carried from unstable continental ice sheet was occupied with the Arctic Ocean during past deglaciation. This is the valuable information to consider the range and scale of the ice sheet collapse in the past deglaciation. However, formative