Sea surface temperatures and stratification of the subpolar north Atlantic during the mid-Pleistocene (Ca. 800-400 ka)

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Author(s): Alonso-Garcia, M.; Sierro, F. J.; Cacho, I.; Flores, J.; Kucera, M.
Author Affiliation(s): Primary:
University of Salamanca, Department of Geology (Paleontology), Salamanca, Spain
University of Barcelona, Spain
Bremen University, Germany
Volume Title: AGU 2012 fall meeting
Source: American Geophysical Union Fall Meeting, Vol.2012; American Geophysical Union 2012 fall meeting, San Francisco, CA, Dec. 3-7, 2012. Publisher: American Geophysical Union, Washington, DC, United States
Note: In English
Summary: The onset of 100-kyr glacial-interglacial cyclicity occurred during the mid-Pleistocene transition (ca. 1.2-0.5 ka), and is linked to important climatic changes, including: intensification of glacial periods, expansion of Northern Hemisphere ice sheets, enhancement of Asian and African aridity, and reorganization of deep ocean circulation. Although multiple hypotheses exist to explain these climatic changes, the detailed forcing mechanisms are not fully understood. To adequately assess these hypotheses, high-resolution multi-proxy reconstructions of high latitude sea surface conditions are required. Here we present a high-resolution study of subpolar North Atlantic sediments from IODP Site U1314 (56 N, 27 W, 2820 m water depth) across four climatic cycles (ca. 800 to 400 ka). We use paired Neogloboquadrina pachyderma sinistral (s) δ18O and Mg/Ca, N. pachyderma dextral (d) δ18O, and planktonic foraminifer assemblage records to improve understanding of subpolar North Atlantic sea surface temperature (SST) and upper water column stratification during the mid-Pleistocene. Planktic foraminifer Mg/Ca paleothermometry has been used successfully to reconstruct SSTs at low to mid-latitudes. However, the cold temperatures at high-latitudes reduce the sensitivity of Mg incorporation into foraminiferal calcite. Several calibration datasets involving N. pachyderma (s) indicate anomalously high Mg/Ca in Arctic and Polar waters that may not reflect temperature but other factors like salinity, alkalinity or calcification depth. Thus, a multi-proxy approach is essential to study past subpolar SSTs. However, we can infer the presence of Arctic waters at Site U1314 tracking the abundance of N. pachyderma (s), which provides a unique opportunity to evaluate the influence of Arctic waters in N. pachyderma (s) Mg/Ca paleothermometry due to the southward migration of the Arctic front across glacial-interglacial cycles. To examine upper water column stratification, we generated N. pachyderma (s) and (d) δ18O records and planktic foraminifer assemblages. N. pachyderma (s) lives at the pycnocline, where the waters are usually close to winter temperatures, whereas N. pachyderma (d) lives in the upper 50-100 m of the water column during summer and autumn periods of stratification. Thus, the offset between the δ18O records may reflect variations in regional thermal stratification, particularly during interglacial periods. Planktic foraminifer assemblages support our δ18O-based interpretations of the upper water column.
Year of Publication: 2012
Research Program: IODP Integrated Ocean Drilling Program
Key Words: 24 Surficial Geology, Quaternary Geology; Atlantic Ocean; Cenozoic; Expedition 306; Expeditions 303/306; IODP Site U1314; Integrated Ocean Drilling Program; Middle Pleistocene; North Atlantic; Northeast Atlantic; Paleo-oceanography; Paleoclimatology; Pleistocene; Quaternary; Sea-surface temperature
Coordinates: N562200 N562200 W0275300 W0275300
Record ID: 2015005652
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