Multi-proxy record of ocean-climate variability during the last two millennia on the Mackenzie Shelf, Beaufort Sea

A 2,000 year-long oceanographic history, in sub-centennial resolution, from a Canadian Beaufort Sea continental shelf site (60 meters water depth) near the Mackenzie River outlet is reconstructed from ostracode and foraminifera faunal assemblages, shell stable isotopes (δ18O, δ13C) and sediment biogenic silica. The chronology of three sediment cores making up the composite section was established using 137Cs and 210Pb dating for the most recent 150 years and combined with linear interpolation of radiocarbon dates from bivalve shells and foraminifera tests. Continuous centimeter-sampling of the multicore and high-resolution sampling of a gravity and piston core yielded a time-averaged faunal record of every ~40 years from 0 to 1850 CE and every ~24 years from 1850 to 2013 CE. Proxy records were consistent with temperature oscillations and related changes in organic carbon cycling associated with the Medieval Climate Anomaly (MCA) and the Little Ice Age (LIA). Abundance changes in dominant microfossil species, such as the ostracode Paracyprideis pseudopunctillata and agglutinated foraminifers Spiroplectammina biformis and S. earlandi, are used as indicators of less saline, and possibly corrosive/turbid bottom conditions associated with the MCA (~800-1200 CE) and the most recent ~60 years (1950-2013). During these periods, pronounced fluctuations in these species suggest that prolonged seasonal sea-ice melting, changes in riverine inputs and sediment dynamics affected the benthic environment. Taxa analyzed for stable oxygen isotope composition of carbonates show the lowest δ18O values during intervals within the MCA and the highest during the late LIA, which is consistent with a 1° to 2°C cooling of bottom waters. Faunal and isotopic changes during the cooler LIA (1300-1850 CE) are most apparent at ~1500-1850 CE and are particularly pronounced during 1850 to ~1900 CE, with a ~0.5 per mil increase in δ18O values of carbonates from median values in the analyzed taxa. This very cold 50-year period suggests that enhanced summer sea ice suppressed productivity, which is indicated by low sediment biogenic silica values and lower δ13C values in analyzed species. From 1900 CE to present, declines in calcareous faunal assemblages and changes in dominant species (Cassidulina reniforme and P. pseudopunctillata) are associated with less hospitable bottom waters, indicated by a peak in agglutinated foraminifera from 1950-1990 CE

Deglacial sea level history of the East Siberian Sea and Chukchi Sea margins

Deglacial (12.8–10.7 ka) sea level history on the East Siberian continental shelf and upper continental slope was reconstructed using new geophysical records and sediment cores taken during Leg 2 of the 2014 SWERUS-C3 expedition. The focus of this study is two cores from Herald Canyon, piston core SWERUS-L2-4-PC1 (4-PC1) and multicore SWERUS-L2-4-MC1 (4-MC1), and a gravity core from an East Siberian Sea transect, SWERUS-L2-20-GC1 (20-GC1). Cores 4-PC1 and 20-GC were taken at 120 and 115 m of modern water depth, respectively, only a few meters above the global last glacial maximum (LGM;  ∼  24 kiloannum or ka) minimum sea level of  ∼  125–130 meters below sea level (m b.s.l.). Using calibrated radiocarbon ages mainly on molluscs for chronology and the ecology of benthic foraminifera and ostracode species to estimate paleodepths, the data reveal a dominance of river-proximal species during the early part of the Younger Dryas event (YD, Greenland Stadial GS-1) followed by a rise in river-intermediate species in the late Younger Dryas or the early Holocene (Preboreal) period. A rapid relative sea level rise beginning at roughly 11.4 to 10.8 ka ( ∼  400 cm of core depth) is indicated by a sharp faunal change and unconformity or condensed zone of sedimentation. Regional sea level at this time was about 108 m b.s.l. at the 4-PC1 site and 102 m b.s.l. at 20-GC1. Regional sea level near the end of the YD was up to 42–47 m lower than predicted by geophysical models corrected for glacio-isostatic adjustment. This discrepancy could be explained by delayed isostatic adjustment caused by a greater volume and/or geographical extent of glacial-age land ice and/or ice shelves in the western Arctic Ocean and adjacent Siberian land areas

Modern and Interglacial Marine Ostracode Species Diversity Patterns off Eastern North America

PC002: Assessing Ecosystem Variability from Paleoceanographic Archives - Session ID 9343: Ref. no. 91649Latitudinal species diversity gradients (LSDGs) are a major feature of various marine groups. However, the detailed shape of LSDG in each marine taxonomic group and the causes of the diversity patterns, notably climatic factors, are still controversial due to limited sampling of many taxa in the world’s oceans. We analyzed benthic podocopid ostracode faunal assemblages on the continental shelf regions from Arctic to tropical regions off eastern North America to determine biodiversity patterns and their relationships to oceanographic conditions (temperature, productivity, etc). Our database consists of 200 ostracode species from more than 100 bottom sediment samples. Preliminary results suggest that biodiversity, as measured using simple diversity (S), rarefaction, Shannon and α-Fisher indices, show strong latitudinal diversity gradients in which diversity is 2 to 3 times higher in tropical and subtropical regions that in northern high latitude areas. These modern ostracode diversity patterns will be compared with those from past interglacial periods of global warmth during the Pliocene and Pleistocene to assess the impact of warmer-than- present climate conditions on diversity

Quaternary ostracoda from the Arctic Ocean: sea ice and ocean circulation variability over orbital timescales

Conference Theme: Back to the FutureScientific Session - Ostracoda in palaeoceanographic reconstructions during the CenozoicThe Arctic is experiencing major changes in sea-ice cover, ocean temperature and marine ecosystems that many hypothesize are caused by anthropogenic influence on polar climate. In order to understand the impacts of climatic change on the Arctic Ocean, it is instructive to examine past climate changes and their impacts. We analyzed ostracode assemblages from six piston cores from the Northwind and Mendeleev Ridges in the Amerasian Basin and the Lomonosov Ridge in the central Arctic to reconstruct paleoceanographic history during Quaternary glacial-interglacial cycles. These cores come from water depths ranging between 700 and 2000 meters and the sediments recovered represent glacial-interglacial cycles of the past 700 ka (kiloannum) including the mid-Brunhes climatic transition ( 700-300 ka). The most important ostracode taxa (and their paleoceanographic significance) include Acetabulastoma arcticum and Pseudocythere caudata (perennial sea ice), Polycope spp. (productivity and sea ice), Krithe glacialis and Henryhowella asperrima (partially sea-ice free conditions, deep water formation), Pterygocythereis vannieuwenhuisei (warm interglacial conditions). Results indicate a seasonally sea-ice free western Arctic during an exceptionally warm interglacial period 400 ka (Marine Isotope Stage 11, MIS 11) and a major faunal turnover at approximately 300 ka when P. vannieuenhuisei became extinct. During this faunal and climatic transition, ostracode assemblages characteristic of interglacial and interstadial periods (MIS 9, 7, 5, 3, 1) first appeared in the Arctic. These changes signify the initial development of interglacial periods characterized by perennial sea ice, such as existed during thelate Holocene interglacial. In addition to orbital-scale paleoceanographic variability, ostracode assemblages vary over millennial timescales, which signify changes in ocean circulation during the glacial, deglacial and interglacial periods.link_to_OA_fulltex

Evaluating response of large-scale shallow marine biodiversity pattern to climate change using micropaleontological records

Session No. 17: T148. Making Paleoecology Relevant to the Twenty-First Centur

Arctic and Western North Atlantic shallow marine diversity patterns: A comparison of controlling factors

Session: Global Environmental Change: GC23A Arctic Environmental Change: Local, Regional, Global Drivers and Impacts II Posters - no. GC23A-1227Shallow marine biodiversity patterns are governed by complicated combinations of environmental factors, and our understanding on the controlling mechanisms remains limited. Here we used ostracodes as a model system to look for the controlling factors on biodiversity patterns in shallow marine environments in the western North Atlantic Ocean and Arctic Ocean continental shelves. We analyzed ostracode biodiversity from 558 sites in the western Atlantic to the Arctic and revealed a negative diversity gradient from the tropics to the Arctic. Regression models and model-averaging results of the latitudinal diversity patterns showed that bottom water temperature is a significant controlling factor of ostracode diversity, whereas bottom water salinity, bottom water pH, bottom water dissolved oxygen, and surface primary productivity may not be. Using the same modelling approach, we will further analyze the Arctic Ocean-wide diversity pattern, which was believed to be controlled by temperature, surface productivity and salinity in other study. We will compare the various factors, which are believed to influence longitudinal diversity variability in the circum-Arctic Ocean, as well as the those that influence latitudinal diversity patterns in North Atlantic Ocean

(Table 2) Radiocarbon ages on Arctic box and multicores

Paleo-sea-ice history in the Arctic Ocean was reconstructed using the sea-ice dwelling ostracode Acetabulastoma arcticum from late Quaternary sediments from the Mendeleyev, Lomonosov, and Gakkel Ridges, the Morris Jesup Rise and the Yermak Plateau. Results suggest intermittently high levels of perennial sea ice in the central Arctic Ocean during Marine Isotope Stage (MIS) 3 (25-45 ka), minimal sea ice during the last deglacial (16-11 ka) and early Holocene thermal maximum (11-5 ka) and increasing sea ice during the mid-to-late Holocene (5-0 ka). Sediment core records from the Iceland and Rockall Plateaus show that perennial sea ice existed in these regions only during glacial intervals MIS 2, 4, and 6. These results show that sea ice exhibits complex temporal and spatial variability during different climatic regimes and that the development of modern perennial sea ice may be a relatively recent phenomenon