Late Pleistocene to Holocene changes in upper-ocean stratification and its impact on marine productivity, sea surface temperatures, and salinity in the subarctic Northwest Pacific

• Main Author: Riethdorf, Jan-Rainer
• Format: Thesis
• Language: English
• Published: 2012
• Subjects: Bering Sea; Kamchatka; Neogloboquadrina pachyderma; okhotsk sea; Planktonic foraminifera; Sea ice; Subarctic
• Online Access: https://oceanrep.geomar.de/id/eprint/15437/; https://oceanrep.geomar.de/id/eprint/15437/1/diss_riethdorf.pdf; http://macau.uni-kiel.de/receive/dissertation_diss_00009259

The modern subarctic North Pacific realm is characterized by a steep vertical gradient in salinity, the permanent halocline. The halocline not only hampers the exchange of gas and heat between the deep ocean and the atmosphere, it also restricts the supply of nutrients from the subsurface into the photic zone, thereby limiting marine productivity. However, for the subarctic North Pacific and its marginal seas it remains unclear whether low glacial productivity was controlled by upper-ocean stratification or by sea-ice dynamics. Recent proxy and modelling studies indicate that the halocline weakened during the last glacial termination. This thesis is based on piston cores recovered from intermediate water levels in the hitherto only poorly studied western Bering Sea, the continental slope off eastern Kamchatka, and the southern Okhotsk Sea. Age models rely on a combination of benthic oxygen isotope stratigraphy, magnetostratigraphy, radiocarbon dating, and intercore correlations via high-resolution core logging data. Millennial-scale changes in marine productivity and terrigenous matter supply were reconstructed over the past 180 kyr applying a geochemical multi-proxy approach in combination with XRF logging data. Special emphasis is given to the last glacial termination, for which high-resolution sea surface temperature (SST), as well as subsurface temperature and salinity-approximating records were produced. These records stem from alkenone-thermometry, and from the combined measurement of stable oxygen isotope and Mg/Ca ratios of the planktonic foraminifera Neogloboquadrina pachyderma (sin.). Direct comparison between both temperature reconstructions allowed to infer oceanographic changes in the mixed layer. Deglacial changes in the ventilation of intermediate and deep waters are inferred from marine radiocarbon ages and stable carbon isotope records. Results point towards low marine productivity but high terrigenous inputs during most of the last glacial-interglacial cycle and Marine Isotope Stage (MIS) 6. ...