Abstracts from the 20th International Symposium on Signal Transduction at the Blood-Brain Barriers

https://deepblue.lib.umich.edu/bitstream/2027.42/138963/1/12987_2017_Article_71.pd

Submillennial variations in ocean conditions during deglaciation based on diatom assemblages from the southwest Atlantic

We present a high-resolution paleoceanographic record of deglaciation based on diatom assemblages from a core located just south of the Polar Front in the southwest Atlantic. Core KC073 is from a sediment drift at the mouth of the Falkland Trough and contains sediments from the Last Glacial Maximum (LGM) to present, dated using radiocarbon dates on bulk organic matter and radiolarian stratigraphy. The site lies along the path of the Antarctic Circumpolar Current (ACC) and immediately downstream of where North Atlantic Deep Water (NADW) is entrained into the ACC. Significant variations in ocean conditions are reflected in high-amplitude changes in diatom concentrations and assemblage composition. The diatom assemblage at the LGM indicates that winter sea ice extent was at least 5° farther north than present until at least 19.0 ka (calendar years) and summer sea ice may have occasionally extended over the site, but for the most part it lay to the south. During deglaciation, Chaetoceros resting spores (CRS) dominate the diatom assemblage with valve concentrations in excess of 500 × 106 valves per gram. Submillennial-scale variations in the numbers of CRS and Thalassiosira antarctica occur throughout the late deglacial and dominate the changes in diatom concentration. We propose that the influx of CRS is controlled by the flow of NADW over the Falkland Plateau. As such our data provide unique evidence that NADW impacted on this sector of the Southern Ocean during deglaciation. During the Holocene the sedimentation rate dramatically reduced. We suggest that the ACC flow increased over the site and inhibited settling and winnowed the surface sediments

Glacial‐interglacial changes in central tropical Pacific surface seawater property gradients

Much uncertainty exists about the state of the oceanic and atmospheric circulation in the tropical Pacific over the last glacial cycle. Studies have been hampered by the fact that sediment cores suitable for study were concentrated in the western and eastern parts of the tropical Pacific, with little information from the central tropical Pacific. Here we present information from a suite of sediment cores collected from the Line Islands Ridge in the central tropical Pacific, which show sedimentation rates and stratigraphies suitable for paleoceanographic investigations. Based on the radiocarbon and oxygen isotope measurements on the planktonic foraminifera Globigerinoides ruber, we construct preliminary age models for selected cores and show that the gradient in the oxygen isotope ratio of G. ruber between the equator and 8 degrees N is enhanced during glacial stages relative to interglacial stages. This stronger gradient could reflect enhanced equatorial cooling (perhaps reflecting a stronger Walker circulation) or an enhanced salinity gradient (perhaps reflecting increased rainfall in the central tropical Pacific)

High resolution reconstruction of Southwest Atlantic sea-ice and its role in the carbon cycle during marine isotope stages 3 and 2

Recent modeling suggests that changes in Southern Ocean sea-ice extent potentially regulated the exchange of CO2 release between the ocean and atmosphere during glacials. Unfortunately, a lack of high-resolution sea-ice records from the Southern Ocean has prevented detailed testing of these model-based hypotheses with field data. Here we present high-resolution records of Southern Ocean sea-ice, for the period 35–15 cal ka BP, derived from diatom assemblages measured in three glacial sediment cores forming an ∼8° transect across the Scotia Sea, southwest Atlantic. Chronological control was achieved through a novel combination of diatom abundance stratigraphy, relative geomagnetic paleointensity data, and down-core magnetic susceptibility and ice core dust correlation. Results showed that the winter sea-ice edge reached its maximum northward extent of ∼53°S, at least 3° north of its modern limit, between ∼25 and ∼23.5 cal ka BP, predating the Last Glacial Maximum (LGM). Maximum northward expansion of the summer sea-ice edge also pre-dated the LGM, advancing to at least 61°S, and possibly as far north as 55°S between ∼31 and ∼23.5 cal ka BP, a ∼12° advance from its modern position. A clear shift in the seasonal sea-ice zone is evident following summer sea-ice edge retreat at ∼23.5 cal ka BP, potentially related to austral insolation forcing. This resulted in an expanded seasonal sea-ice zone between ∼22.5 cal ka BP and deglaciation. Our field data confirm that Southern Ocean sea-ice had the physical potential to influence the carbon cycle both as a physical barrier and more importantly through the suppression of vertical mixing and cycling of pre-formed nutrients. Our data indicates that Southern Ocean sea-ice was most effective as a physical barrier between ∼31 and ∼23.5 cal ka BP and as a mechanism capable of reducing vertical mixing between ∼22.5 cal ka BP and deglaciation. However, poor correlations with atmospheric CO2 variability recorded in ice cores, particularly the lack of a CO2 response during a rapid sea-ice meltback event, recorded at our study sites at the same time as Antarctic Isotopic Maximum 2, suggest that Southern Ocean sea-ice in the Scotia Sea did not play a controlling role in atmospheric CO2 variation during the glacial