Holocene history of Pacific Water flux through Bering Strait recorded by smectite abundance and ɛNd-signature in a southern Chukchi Sea cored sequence (original) (raw)
Related papers
Paleoceanography, 2012
Millennial-scale variability in the behavior of North Pacific Intermediate Water during the last glacial and deglacial period, and its association with Dansgaard-Oeschger (D-O) cycles and Heinrich events, are examined based on benthic foraminiferal oxygen and carbon isotopes (d 18 O bf and d 13 C bf) and %CaCO 3 using a sediment core recovered from the northeastern slope of the Bering Sea. A suite of positive d 18 O bf excursions at intermediate depths of the Bering Sea, which seem at least in part associated with increases in the d 18 O bf gradients between the Bering and Okhotsk Seas, suggest the Bering Sea as a proximate source of intermediate water during several severe stadial episodes in the last glacial and deglacial period. Absence of such d 18 O bf gradients during periods of high surface productivity in the Bering and Okhotsk Seas, which we correlate to DO interstadials, suggests a reduction in intermediate water production in the Bering Sea and subsequent introduction of nutrient-rich deep waters from the North Pacific into intermediate depths of the Bering Sea. We argue that a reorganization of atmospheric circulation in the high-latitude North Pacific during severe cold episodes in the last glacial and deglacial period created favorable conditions for brine rejection in the northeastern Bering Sea. The resulting salinity increase in the cold surface waters could have initiated intermediate (and deep) water formation that spread out to the North Pacific.
IODP Expedition 323 – Pliocene and Pleistocene Paleoceanographic Changes in the Bering Sea
Scientific Drilling, 2011
High-resolution paleoceanography of the Plio-Pleistocene is important in understanding climate forcing mechanisms and the associated environmental changes. This is particularly true in high-latitude marginal seas such as the Bering Sea, which has been very sensitive to changes in global climate during interglacial and glacial or Milankovitch time scales. This is due to significant changes in water circulation, land-ocean interaction, and sea-ice formation. With the aim to reveal the climate and oceanographic history of the Bering Sea over the past 5 Ma, Integrated Ocean Drilling Program (IODP) Expedition 323 cored a total of 5741 meters of sediment (97.4% recovery) at seven sites covering three different areas: Umnak Plateau, Bowers Ridge, and the Bering slope region. Four deep holes range from 600 m to 745 m spanning in age from 1.9 Ma to 5 Ma. The water depths (819 m to 3173 m) allow characterization of past vertical water mass distribution such as the oxygen minimum zone (OMZ). The results highlight three key points. (1) The first is an understanding of long-term evolution of surface-water mass distribution during the past 5 Ma including past sea-ice distribution and warm and less eutrophic subarctic Pacific water mass entry into the Bering Sea.
Pliocene cooling enhanced by flow of low-salinity Bering Sea water to the Arctic Ocean
Nature communications, 2015
Warming of high northern latitudes in the Pliocene (5.33-2.58 Myr ago) has been linked to the closure of the Central American Seaway and intensification of North Atlantic Deep Water. Subsequent cooling in the late Pliocene may be related to the effects of freshwater input from the Arctic Ocean via the Bering Strait, disrupting North Atlantic Deep Water formation and enhancing sea ice formation. However, the timing of Arctic freshening has not been defined. Here we present neodymium and lead isotope records of detrital sediment from the Bering Sea for the past 4.3 million years. Isotopic data suggest the presence of Alaskan glaciers as far back as 4.2 Myr ago, while diatom and C37:4 alkenone records show a long-term trend towards colder and fresher water in the Bering Sea beginning with the M2 glaciation (3.3 Myr ago). We argue that the introduction of low-salinity Bering Sea water to the Arctic Ocean by 3.3 Myr ago preconditioned the climate system for global cooling.
Sedimentary proxies for Pacific water inflow through the Herald Canyon, western Arctic Ocean
arktos, 2018
Pacific water inflow to the Arctic Ocean occurs through the shallow Bering Strait. With a present sill depth of only 53 m, this gateway has been frequently closed during glacial sea-level low stands of the Pleistocene. Here, we investigate the sedimentological and mineralogical response to sea-level rise and the opening of the Bering Strait during the last deglaciation in a 6.1 m-long marine sediment core (SWERUS-L2-4-PC1) from the Herald Canyon. Grain size data indicate an abrupt erosional contact at 412 cm down core that likely formed when Pacific waters first started to flow into the Arctic Ocean around 11 cal ka BP, and was topographically steered into the Herald Canyon. A transitional unit between 412 and 390 cm appears to be a condensed interval with minimal local sedimentation. The underlying sediments, deposited in a shallow, river-proximal setting, exhibit a rather uniform bulk and clay mineral composition similar to mineral assemblages from surface sediment samples of the ...
A large sediment deposit known as the Meiji Drift, located in the northwestern Pacific Ocean, is thought to have formed from deep water exiting the Bering Sea, although no notable deep water forms there presently. We determine the terrigenous sources since 140 ka to the drift using bulk sediment 40 Ar-39 Ar and Nd isotopic analyses on the silt-sized (20-63 μm) terrigenous fraction from Ocean Drilling Program (ODP) Site 884 to reconstruct paleo-circulation patterns. There are large changes in both isotopic tracers, varying on glacialinterglacial cycles. During glacial intervals, bulk sediment 40 Ar-39 Ar ages range between 40 and 80 Ma, while Nd isotopic values range from ε Nd = −1 to +2. During interglacial intervals, sediments become much younger and more radiogenic, with bulk sediment ages falling to 2-15 Ma and Nd isotopic values ranging between ε Nd =+5 and +9. These data and quantitative comparison to potential source rocks indicate that the young Kamchatkan and Aleutian Arcs, lying NW and NE of the Meiji Drift, contribute the majority of sediment during interglacials. Conversely, older source rocks, such as those drained by the Yukon River and northeast Russia are the dominant origin of sediments during glacials. Mixing model calculations suggest that as much as 35-45% of the sediment deposited in the Meiji Drift during glacials is from the Bering Sea. It remains unclear whether thermohaline-type circulation or focussing of Bering Sea flow lead to the glacial-interglacial sediment source changes observed here.
Global and Planetary Change, 2001
Three cores recovered off the northwest of Svalbard were studied with respect to glacialrinterglacial changes of clay and Ž . bulk mineralogy, lithology and organic geochemistry. The cores cover the Late Quaternary Marine Isotope Stages MIS 6-1 Ž . ca. 170,000 years and are located in the vicinity of the Polar Front which separates the warm Atlantic water of the Westspitsbergen Current and the cold Polar Water of the Transpolar Drift. Globally driven changes in the paleoenvironment like the variable advection of warm Atlantic water into the Arctic Ocean can be distinguished from regional events by means of source mineral signatures and organic geochemistry data. In particular, a combination of high organic carbon and low carbonate contents, high CrN-ratios, a particular lithology and a distinct bulk and clay mineral assemblage can be related to Svalbard ice sheet developments between 23,000 and 19,500 14 C years. This complex sediment pattern has been traced to the northwest of Spitsbergen as far north as 828N. Additionally, the same signature has been recognized in detail in upper MIS 5 sediments. The striking similarity of the history of the SvalbardrBarents Sea Ice Sheet during the late and earlyrmiddle Weichselian is elaborated. Both sediment horizons are intercalated between biogenic calcite rich core sequences which contain the so-called AHigh Productivity ZonesB or ANordway EventsB related to the increased advection of warm Atlantic water to the Arctic Ocean. This study provides further evidence that the meridional circulation pattern has been present during most of the Weichselian and that the ice cover was often reduced in the northeastern Fram Strait and above the Yermak Plateau. Our findings contradict the widely used reconstructions in modelling of the last glaciation cycle and reveal a much more dynamic system in the Fram Strait and southwestern Eurasian Basin of the Arctic Ocean. q
Deep Sea Research Part II: Topical Studies in Oceanography, 2016
Late Pliocene to early Pleistocene paleoproductivity changes in the Bering Sea were reconstructed using geochemical concentrations and mass accumulation rates (MARs) of CaCO 3 , biogenic opal, and total organic carbon (TOC), and sedimentary nitrogen isotope ratios (į 15 N) at IODP Expedition 323 Hole U1343E, drilled in the northern slope area (1956 m deep) of the Bering Sea. CaCO 3 concentration is generally low, but prominent CaCO 3 peaks occur intermittently due to subseafloor authigenic carbonate formation rather than biogenic accumulation, regardless of glacial-interglacial variations. Biogenic opal concentrations reflect orbital-scale glacial-interglacial variations. However, TOC concentration did not show clear glacial-interglacial variation, probably due to poor preservation. The sedimentary į 15 N values vary synchronously with biogenic opal concentration on orbital timescales. The co-varying pattern of opal productivity and į 15 N values at Hole U1343E is a result of nutrient utilization controlled by diatom productivity in the Bering slope area where Fe is not a limiting factor. Biogenic opal and TOC MARs showed a temporal shift at around 1.9 Ma from a high productivity period under nutrientenriched conditions to a low productivity period under relatively nutrient-depleted conditions. High diatom productivity with low į 15 N values before 1.9 Ma is associated with abundant nutrient supply by upwelling in relation to strong surface current system. This productivity decrease at about 1.9 Ma was also found in the southern Bering Sea (Site U1341) and may be related to global opal reorganization.