- Email: [email protected]
Response of diatom and silicoflagellate assemblages to climate change in the Santa Barbara basin during the past 178 years and the rise of the toxic diatom Pseudo-nitzschia australis
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Abstracts / Quaternary International 310 (2013) 227–246
records. Here we present a high-resolution middle and late Holocene charcoal record to augment existing pollen and diatom data from Favre Lake in the Ruby Mountains, Nevada (40 260 39.8000 N,115 200 49.500 W, 2899 m asl). High concentrations of charcoal corresponding to diatom and pollen data indicate rising lake level are interpreted as reflective of sustained summer precipitation and a strengthened southwestern monsoon at around 5400 cal yr BP. These conditions may have supported an increase in fire intensity and frequency as a result of increased fuel buildup and frequent lightning. Lower and more variable charcoal concentrations after approximately 4000 cal yr BP, concurrent with relatively quiescent pollen and diatom assemblages, suggests the influence of a strengthening and increasingly variable ENSO, resulting in a shift to a more variable, lower intensity fire regime. THE IMPACT OF LITTLE ICE AGE COOLING ON MOUNTAIN HEMLOCK (TSUGA MERTENSIANA) DISTRIBUTION IN SOUTHCENTRAL, ALASKA R. Scott Anderson a, Darrell S. Kaufman a, Caleb Schiff a, Tom Daigle b, Edward Berg c. a School of Earth Sciences and Environmental Sustainability, Northern Arizona University, Flagstaff, AZ 86011, USA; b GEI Consultants, 4601 DTC Boulevard, Suite 900, Denver, CO 80237, USA; c US Fish and Wildlife Service, Kenai National Wildlife Refuge, PO Box 2139, Soldotna, AK 99669, USA (retired) E-mail address: [email protected]. The natural distribution of mountain hemlock (Tsuga mertensiana) in the northeast Pacific is in regions of cool to cold maritime climate, with cool winters and short summers. Presently, the species reaches its northern distribution in southcentral Alaska. We investigated the Holocene history of vegetation and climate change for two sites in and near the Kenai Mountains, south of Anchorage. Mica Lake is located at 100 m elevation on an island in Prince William Sound, near the northern limits of the tree, whereas Goat Lake is located at 550 m elevation, in the Kenai Mountains, at the upper local limit of mountain hemlock. From pollen analysis of these lake sediments, mountain hemlock became established at Mica Lake by at least 6000 cal yr BP. The tree became established at the higher elevation Goat Lake sometime after 3000 years ago. Expansion at both sites was abruptly curtailed during the colder climate of the Little Ice Age, commencing at Goat Lake in the mid17th century. The decline was more extensive at the Goat Lake site, where climatic conditions may have been severe enough to reduce or eliminate the mountain hemlock forest there. This is consistent with tree-ring evidence of major glacial advance (Wiles and Calkin, 1993; 1994; Daigle and Kaufman, 2008; Wiles et al., 2009) at this time in the Kenai Mountains. Warmer conditions during the 20th century have reversed that trend. Daigle, T.A., Kaufman, D.S., 2009. Holocene Climate inferred from glacier extent, lake sediment and tree rings at Goat Lake, Kenai Mountains, Alaska, USA. Journal of Quaternary Science 24, 33–45. Wiles, G.C., Calkin, P.E., 1993. Neoglacial fluctuations and sedimentation of an iceberg-calving glacier resolved with tree rings (Kenai Fjords National Park, Alaska). Quaternary International 18, 35–42. Wiles, G.C., Calkin, P.E., 1994. Late Holocene, high-resolution glacial chronologies and climate, Kenai Mountains, Alaska. Geological Society of America Bulletin, 106, 281-303. Wiles, G.C., Barclay, D.J., Calkin, P.E., Lowell, T.V., 2008. Century to Millennial-Scale Temperature Variations for the Last Two Thousand Years Inferred from Glacial Geologic Records of Southern Alaska. Global and Planetary Change. 57. doi:10.1016/j.gloplacha.2006.07.036. RESPONSE OF DIATOM AND SILICOFLAGELLATE ASSEMBLAGES TO CLIMATE CHANGE IN THE SANTA BARBARA BASIN DURING THE PAST 178 YEARS AND THE RISE OF THE TOXIC DIATOM PSEUDO-NITZSCHIA AUSTRALIS John A. Barron a, David Bukry a, David B. Field b. a Volcano Science Center, MS 910, US Geological Survey, Menlo Park, CA 94025, USA; b Department of Natural Sciences, Hawaii Pacific University, Kaneohe, HI 96744, USA E-mail address: [email protected].
Diatoms and silicoflagellate assemblages studied in two year-increments of varved samples in Santa Barbara Basin (SBB) box core 0806 spanning 1830
to 2007 suggest that unprecedented warming of surface waters began at about 1940, which is in agreement with CalCOFI SST data and changes in planktonic foraminiferal assemblages. These earlier studies argued that increased stratification and deepening of the thermocline occurred during the latter half of the 20th century within 50-100 km of the southern California coast in response to anthropogenically-forced global warming. Diatoms (Thalassionema nitzschioides ¼ TN) and silicoflagellates (Distephanus speculum s.l. ¼ DS) indicative of cooler waters and a shallow thermocline declined markedly in relative numbers in the SBB beginning at about 1940. Prior to that time, TN constituted on average w30% of the Chaetoceros-free diatom sediment assemblage and DS on average w36% of the silicoflagellate assemblage. Between 1940 and 1996 these relative abundances drop to w20% (TN) and w8% (DS). Cooling of surface waters coincident with the onset of negative PDO conditions in the North Pacific in 1998 brought about a return to pre-1940 values of these cool water taxa (TN w31%, DS w25%). However, this recent regional cooling appears to have been accompanied by profound changes to surface water productivity events in the SBB. Pseudonitzschia australis, a diatom associated with domoic acid, a neurotoxin that causes shellfish poisoning and marine mammal deaths, appeared suddenly in the SBB sediment record in 1999 and increased significantly in numbers as a bloom-forming taxon (relatively to Chaetoceros spores) in 2003. Prior to 2003 diatom blooms represented in the SBB sediment record consisted predominantly of Chaetoceros spores and less commonly of Rhizosolenia spp. (Neocalyptrella robusta and R. setigera). Fecal pellets dominated by valves of P. australis, however, are abundant in both the 2003 and 2006 samples, coincident with recorded incidents of domoic acid increase and widespread shellfish poisoning in the SBB. According to published studies the first recorded large-scale toxigenic P. australis bloom in the SBB occurred in June 1998 as part of more widespread blooms and shellfish poisoning along the central California coast. Although high numbers (or blooms) of P. australis were reported in plankton studies off the Scripps Pier in La Jolla during the 1930's, 1967, and 1983, blooms of P. australis associated with toxic domoic acid levels were first reported in 1991 in Monterey Bay. Biologists have shown that Pseudo-nitzschia blooms correspond to lowered sea surface temperatures and increased salinity that are typical of coastal upwelling events, but they have debated whether increased nutrients levels from river runoff have been a factor in the recent increase of these blooms. Laboratory studies have demonstrated that toxin production in some species of Pseudo-nitzschia may increase under silicic acid or phosphorous limitation. Whatever the cause, our 178 year-long diatom sediment record suggests that the recent increase of Pseudo-nitzschia blooms in the SBB has occurred at the expense of Chaetoceros and Rhizosolenia, the natural bloom-forming diatoms in the SBB. EXTENDING THE RECORD OF ABRUPT AND MILLENNIAL-SCALE CLIMATE AND OCEAN CHANGE THROUGH THE MID-PLEISTOCENE TRANSITION IN SANTA BARBARA BASIN, CALIFORNIA Richard J. Behl a, Sara Afshar a, James P. Kennett b, Craig Nicholson c, Christopher C. Sorlien b, Courtney J. Marshall a, Tessa M. Hill c, Sarah M. White c, Walter E. Dean d, John A. Barron e. a Department of Geological Sciences, California State University, Long Beach, CA 90840, USA; b Department of Earth Science, University of California, Santa Barbara, CA 93106, USA; c Department of Geology, University of California, Davis, CA 9561, USA; d US Geological Survey, Federal Center, PO Box 25046, Denver, CO 80225, USA; e US Geological Survey, 345 Middlefield Road, Menlo Park, CA 94025, USA E-mail address: [email protected].
Quaternary strata in the Santa Barbara basin, California, hold the potential to extend subdecadal-resolution paleoclimate records back through the Mid-Pleistocene Transition (>1 Ma). In support of proposed continuous coring by IODP, we conducted an integrated seismic acquisition and piston coring campaign in 2005 and 2008 where we acquired >40 2-11 m piston cores that provide w2000–9000 year windows into past climate behavior. We identified and mapped distinctive seismic stratigraphic horizons across the basin to seafloor outcrop in pre-existing multichannel seismic (MCS) reflection data and in high-resolution MCS and towed chirp data acquired during our research cruises. Horizons and cores are dated by interpolation between ODP Site 893, a previously published 1-Ma horizon,
Abstracts / Quaternary International 310 (2013) 227–246
records. Here we present a high-resolution middle and late Holocene charcoal record to augment existing pollen and diatom data from Favre Lake in the Ruby Mountains, Nevada (40 260 39.8000 N,115 200 49.500 W, 2899 m asl). High concentrations of charcoal corresponding to diatom and pollen data indicate rising lake level are interpreted as reflective of sustained summer precipitation and a strengthened southwestern monsoon at around 5400 cal yr BP. These conditions may have supported an increase in fire intensity and frequency as a result of increased fuel buildup and frequent lightning. Lower and more variable charcoal concentrations after approximately 4000 cal yr BP, concurrent with relatively quiescent pollen and diatom assemblages, suggests the influence of a strengthening and increasingly variable ENSO, resulting in a shift to a more variable, lower intensity fire regime. THE IMPACT OF LITTLE ICE AGE COOLING ON MOUNTAIN HEMLOCK (TSUGA MERTENSIANA) DISTRIBUTION IN SOUTHCENTRAL, ALASKA R. Scott Anderson a, Darrell S. Kaufman a, Caleb Schiff a, Tom Daigle b, Edward Berg c. a School of Earth Sciences and Environmental Sustainability, Northern Arizona University, Flagstaff, AZ 86011, USA; b GEI Consultants, 4601 DTC Boulevard, Suite 900, Denver, CO 80237, USA; c US Fish and Wildlife Service, Kenai National Wildlife Refuge, PO Box 2139, Soldotna, AK 99669, USA (retired) E-mail address: [email protected]. The natural distribution of mountain hemlock (Tsuga mertensiana) in the northeast Pacific is in regions of cool to cold maritime climate, with cool winters and short summers. Presently, the species reaches its northern distribution in southcentral Alaska. We investigated the Holocene history of vegetation and climate change for two sites in and near the Kenai Mountains, south of Anchorage. Mica Lake is located at 100 m elevation on an island in Prince William Sound, near the northern limits of the tree, whereas Goat Lake is located at 550 m elevation, in the Kenai Mountains, at the upper local limit of mountain hemlock. From pollen analysis of these lake sediments, mountain hemlock became established at Mica Lake by at least 6000 cal yr BP. The tree became established at the higher elevation Goat Lake sometime after 3000 years ago. Expansion at both sites was abruptly curtailed during the colder climate of the Little Ice Age, commencing at Goat Lake in the mid17th century. The decline was more extensive at the Goat Lake site, where climatic conditions may have been severe enough to reduce or eliminate the mountain hemlock forest there. This is consistent with tree-ring evidence of major glacial advance (Wiles and Calkin, 1993; 1994; Daigle and Kaufman, 2008; Wiles et al., 2009) at this time in the Kenai Mountains. Warmer conditions during the 20th century have reversed that trend. Daigle, T.A., Kaufman, D.S., 2009. Holocene Climate inferred from glacier extent, lake sediment and tree rings at Goat Lake, Kenai Mountains, Alaska, USA. Journal of Quaternary Science 24, 33–45. Wiles, G.C., Calkin, P.E., 1993. Neoglacial fluctuations and sedimentation of an iceberg-calving glacier resolved with tree rings (Kenai Fjords National Park, Alaska). Quaternary International 18, 35–42. Wiles, G.C., Calkin, P.E., 1994. Late Holocene, high-resolution glacial chronologies and climate, Kenai Mountains, Alaska. Geological Society of America Bulletin, 106, 281-303. Wiles, G.C., Barclay, D.J., Calkin, P.E., Lowell, T.V., 2008. Century to Millennial-Scale Temperature Variations for the Last Two Thousand Years Inferred from Glacial Geologic Records of Southern Alaska. Global and Planetary Change. 57. doi:10.1016/j.gloplacha.2006.07.036. RESPONSE OF DIATOM AND SILICOFLAGELLATE ASSEMBLAGES TO CLIMATE CHANGE IN THE SANTA BARBARA BASIN DURING THE PAST 178 YEARS AND THE RISE OF THE TOXIC DIATOM PSEUDO-NITZSCHIA AUSTRALIS John A. Barron a, David Bukry a, David B. Field b. a Volcano Science Center, MS 910, US Geological Survey, Menlo Park, CA 94025, USA; b Department of Natural Sciences, Hawaii Pacific University, Kaneohe, HI 96744, USA E-mail address: [email protected].
Diatoms and silicoflagellate assemblages studied in two year-increments of varved samples in Santa Barbara Basin (SBB) box core 0806 spanning 1830
to 2007 suggest that unprecedented warming of surface waters began at about 1940, which is in agreement with CalCOFI SST data and changes in planktonic foraminiferal assemblages. These earlier studies argued that increased stratification and deepening of the thermocline occurred during the latter half of the 20th century within 50-100 km of the southern California coast in response to anthropogenically-forced global warming. Diatoms (Thalassionema nitzschioides ¼ TN) and silicoflagellates (Distephanus speculum s.l. ¼ DS) indicative of cooler waters and a shallow thermocline declined markedly in relative numbers in the SBB beginning at about 1940. Prior to that time, TN constituted on average w30% of the Chaetoceros-free diatom sediment assemblage and DS on average w36% of the silicoflagellate assemblage. Between 1940 and 1996 these relative abundances drop to w20% (TN) and w8% (DS). Cooling of surface waters coincident with the onset of negative PDO conditions in the North Pacific in 1998 brought about a return to pre-1940 values of these cool water taxa (TN w31%, DS w25%). However, this recent regional cooling appears to have been accompanied by profound changes to surface water productivity events in the SBB. Pseudonitzschia australis, a diatom associated with domoic acid, a neurotoxin that causes shellfish poisoning and marine mammal deaths, appeared suddenly in the SBB sediment record in 1999 and increased significantly in numbers as a bloom-forming taxon (relatively to Chaetoceros spores) in 2003. Prior to 2003 diatom blooms represented in the SBB sediment record consisted predominantly of Chaetoceros spores and less commonly of Rhizosolenia spp. (Neocalyptrella robusta and R. setigera). Fecal pellets dominated by valves of P. australis, however, are abundant in both the 2003 and 2006 samples, coincident with recorded incidents of domoic acid increase and widespread shellfish poisoning in the SBB. According to published studies the first recorded large-scale toxigenic P. australis bloom in the SBB occurred in June 1998 as part of more widespread blooms and shellfish poisoning along the central California coast. Although high numbers (or blooms) of P. australis were reported in plankton studies off the Scripps Pier in La Jolla during the 1930's, 1967, and 1983, blooms of P. australis associated with toxic domoic acid levels were first reported in 1991 in Monterey Bay. Biologists have shown that Pseudo-nitzschia blooms correspond to lowered sea surface temperatures and increased salinity that are typical of coastal upwelling events, but they have debated whether increased nutrients levels from river runoff have been a factor in the recent increase of these blooms. Laboratory studies have demonstrated that toxin production in some species of Pseudo-nitzschia may increase under silicic acid or phosphorous limitation. Whatever the cause, our 178 year-long diatom sediment record suggests that the recent increase of Pseudo-nitzschia blooms in the SBB has occurred at the expense of Chaetoceros and Rhizosolenia, the natural bloom-forming diatoms in the SBB. EXTENDING THE RECORD OF ABRUPT AND MILLENNIAL-SCALE CLIMATE AND OCEAN CHANGE THROUGH THE MID-PLEISTOCENE TRANSITION IN SANTA BARBARA BASIN, CALIFORNIA Richard J. Behl a, Sara Afshar a, James P. Kennett b, Craig Nicholson c, Christopher C. Sorlien b, Courtney J. Marshall a, Tessa M. Hill c, Sarah M. White c, Walter E. Dean d, John A. Barron e. a Department of Geological Sciences, California State University, Long Beach, CA 90840, USA; b Department of Earth Science, University of California, Santa Barbara, CA 93106, USA; c Department of Geology, University of California, Davis, CA 9561, USA; d US Geological Survey, Federal Center, PO Box 25046, Denver, CO 80225, USA; e US Geological Survey, 345 Middlefield Road, Menlo Park, CA 94025, USA E-mail address: [email protected].
Quaternary strata in the Santa Barbara basin, California, hold the potential to extend subdecadal-resolution paleoclimate records back through the Mid-Pleistocene Transition (>1 Ma). In support of proposed continuous coring by IODP, we conducted an integrated seismic acquisition and piston coring campaign in 2005 and 2008 where we acquired >40 2-11 m piston cores that provide w2000–9000 year windows into past climate behavior. We identified and mapped distinctive seismic stratigraphic horizons across the basin to seafloor outcrop in pre-existing multichannel seismic (MCS) reflection data and in high-resolution MCS and towed chirp data acquired during our research cruises. Horizons and cores are dated by interpolation between ODP Site 893, a previously published 1-Ma horizon,