scholarly journals Controls on Terrigenous Detritus Deposition and Oceanography Changes in the Central Okhotsk Sea Over the Past 1550 ka

2021 ◽  
Vol 9 ◽  
Author(s):  
Yu-Min Chou ◽  
Xiaodong Jiang ◽  
Li Lo ◽  
Liang-Chi Wang ◽  
Teh-Quei Lee ◽  
...  
Keyword(s):  
Sea Ice ◽  
North Pacific ◽  
Asian Summer Monsoon ◽  
Intermediate Water ◽  
Okhotsk Sea ◽  
The Past ◽  
The North ◽  
Ice Coverage ◽  
Marine Productivity ◽  
The North Pacific

The Okhotsk Sea, which connects the high latitude Asian continent and the North Pacific, plays an important role in modern and past climate changes due to seasonal sea ice coverage and as a precursor of the North Pacific Intermediate Water. The long-term glacial-interglacial changes of sea ice coverage and its impacts on terrigenous transport and surface primary productivity in the Okhotsk Sea remain, however, not well constrained. Base on the paleomagnetic, rock magnetic, micropaleontological (diatom), and geochemical studies of the marine sediment core MD01-2414 (53°11.77′N, 149°34.80′E, water depth: 1,123 m) taken in the central Okhotsk Sea, we reconstruct the terrigenous sediment transport and paleoceanographic variations during the past 1550 thousand years (kyr). Seventeen geomagnetic excursions are identified from the paleomagnetic directional record. Close to the bottom of the core, an excursion was observed, which is proposed to be the Gilsa event ∼1550 thousand years ago (ka). During glacial intervals, our records reveal a wide extension of sea ice coverage and low marine productivity. We observed ice-rafted debris from mountain icebergs composed of coarse and high magnetic terrigenous detritus which were derived from the Kamchatka Peninsula to the central Okhotsk basin. Still during glacial intervals, the initiation (i.e., at ∼900 ka) of the Mid-Pleistocene Transition marks the changes to even lower marine productivity, suggesting that sea-ice coverage became larger during the last 900 ka. During interglacial intervals, the central Okhotsk Sea was either devoid of sea-ice or the ice was at best seasonal; resulting in high marine productivity. The weaker formation of Okhotsk Sea Intermediate Water, lower ventilation, and microbial degradation of organic matter depleted the oxygen concentration in the bottom water and created a reduced environment condition in the sea basin. The freshwater supplied by snow or glacier melting from Siberia and Kamchatka delivered fine grain sediments to the Okhotsk Sea. During the stronger interglacial intervals after the Mid-Brunhes Transition (i.e., Marine Isotope Stages 1, 5e, 9, and 11), strong freshwater discharges from Amur River drainage area are in association with intensified East Asian Summer Monsoon. This process may have enhanced the input of fine-grained terrigenous sediments to the central Okhotsk Sea.

scholarly journals Roles of the Okhotsk Sea and Gulf of Alaska in forming the North Pacific Intermediate Water

2000 ◽  
Vol 105 (C2) ◽  
pp. 3253-3280 ◽  
Author(s):  
Yuzhu You ◽  
Nobuo Suginohara ◽  
Masao Fukasawa ◽  
Ichiro Yasuda ◽  
Ikuo Kaneko ◽  
...  
Keyword(s):  
North Pacific ◽  
Gulf Of Alaska ◽  
Intermediate Water ◽  
Okhotsk Sea ◽  
North Pacific Intermediate Water ◽  
The North ◽  
The North Pacific

scholarly journals The North Pacific Oxygen Uptake Rates over the Past Half Century

2015 ◽  
Vol 29 (1) ◽  
pp. 61-76 ◽  
Author(s):  
Eun Young Kwon ◽  
Curtis Deutsch ◽  
Shang-Ping Xie ◽  
Sunke Schmidtko ◽  
Yang-Ki Cho
Keyword(s):  
North Pacific ◽  
Intermediate Water ◽  
Density Range ◽  
Mode Water ◽  
Half Century ◽  
The Past ◽  
The North ◽  
Past Half Century ◽  
The North Pacific ◽  
Past Half

Abstract The transport of dissolved oxygen (O2) from the surface ocean into the interior is a critical process sustaining aerobic life in mesopelagic ecosystems, but its rates and sensitivity to climate variations are poorly understood. Using a circulation model constrained to historical variability by assimilation of observations, the study shows that the North Pacific thermocline effectively takes up O2 primarily by expanding the area through which O2-rich mixed layer water is detrained into the thermocline. The outcrop area during the critical winter season varies in concert with the Pacific decadal oscillation (PDO). When the central North Pacific Ocean is in a cold phase, the winter outcrop window for the central mode water class (CMW; a neutral density range of γ = 25.6–26.6) expands southward, allowing more O2-rich surface water to enter the ocean’s interior. An increase in volume flux of water to the CMW density class is partly compensated by a reduced supply to the shallower densities of subtropical mode water (γ = 24.0–25.5). The thermocline has become better oxygenated since the 1980s partly because of strong O2 uptake. Positive O2 anomalies appear first near the outcrop and subsequently downstream in the subtropical gyre. In contrast to the O2 variations within the ventilated thermocline, observed O2 in intermediate water (density range of γ = 26.7–27.2) shows a declining trend over the past half century, a trend not explained by the open ocean water mass formation rate.

The North Pacific in Warm(ing) Climates: effects on ocean circulation and biogeochemical cycles

2020 ◽  
Author(s):  
Lester Lembke-Jene ◽  
Ralf Tiedemann ◽  
Dirk Nürnberg ◽  
Xun Gong ◽  
Jianjun Zou ◽  
...  
Keyword(s):  
Boundary Conditions ◽  
North Pacific ◽  
World Ocean ◽  
Biogeochemical Cycles ◽  
Upper Ocean ◽  
Intermediate Water ◽  
Okhotsk Sea ◽  
Ocean Stratification ◽  
The North ◽  
The North Pacific

<p>The North Pacific hosts the both one of the largest oceanic reservoirs of sequestered carbon and extensive oxygen minimum zones in the world ocean, which will likely intensify and expand under future climate warming scenarios, yielding significant consequences for ecosystems, biogeochemical cycles, and living resources. At present, relatively better-oxygenated subsurface North Pacific Intermediate Water (NPIW) mitigates OMZ development, but on instrumental time scales, data the past decades indicate decreasing NPIW ventilation, induced by a freshening and increased stratification of surface and thermocline waters. Longer variations in these oceanographic boundary conditions were, however, large and are thus able to hinder assessment of anthropogenic influences against natural background shifts. We previously provided evidence modern well-ventilated waters underwent significant millennial-scale variations over the last ca. 12,000 years (Lembke-Jene et al., 2018), with a prominent “tipping point” around 4,500 years before present.Crossing such mid-Holocene threshold led to the Okhotsk Sea becoming the modern ventilation source it is today, although the underlying forcing and physical boundary conditions characteristics remain largely enigmatic. A combination of sea ice loss, higher water temperatures, and remineralization rates may be able to induce a nonlinear change into a different mean state in this region. To constrain these factors we present combined surface, mesopelagic and bathyal ocean proxy records from key study sites in the Western Subarctic Pacific, the Okhotsk Sea and Bering Sea, and the Gulf of Alalska, with submillennial-scale resolution to assess changes in upper ocean stratification, nutrient characteristics and resulting changes on mid-depth water ventilation. Our results imply that under assumed past hemispheric warmer- than-present conditions, regional surface temperatures and upper ocean stratification were increased and changed in a nonlinear mode during the last 4-5,000 years, associated with changing primary productivity patterns and biogeochemical feedback mechanisms. Results from complementary Earth System Model simulations provide evidence for the interaction between the high-latitude North Pacific marginal seas and thePacific Western Subarctic Gyre circulation, with effects on mesopelagic ventilation dynamics and its consequences for large oceanic regions.</p>

Did a Beringian ice sheet once exist?

2020 ◽  
Author(s):  
Zhongshi Zhang ◽  
Qing Yan ◽  
Ran Zhang ◽  
Florence Colleoni ◽  
Gilles Ramstein ◽  
...  
Keyword(s):  
North Pacific ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Climate Modelling ◽  
Mountain Glaciers ◽  
The Past ◽  
The North ◽  
Paleoclimate Records ◽  
Glacial Landforms ◽  
The North Pacific

<p>Did a Beringian ice sheet once exist? This question was hotly debated decades ago until compelling evidence for an ice-free Wrangel Island excluded the possibility of an ice sheet forming over NE Siberia-Beringia during the Last Glacial Maximum (LGM). Today, it is widely believed that during most Northern Hemisphere glaciations only the Laurentide-Eurasian ice sheets across North America and Northwest Eurasia became expansive, while Northeast Siberia-Beringia remained ice-sheet-free. However, recent recognition of glacial landforms and deposits on Northeast Siberia-Beringia and off the Siberian continental shelf has triggered a new round of debate.These local glacial features, though often interpreted as local activities of ice domes on continental shelves and mountain glaciers on continents,   could be explained as an ice sheet over NE Siberia-Beringia. Only based on the direct glacial evidence, the debate can not be resolved. Here, we combine climate and ice sheet modelling with well-dated paleoclimate records from the mid-to-high latitude North Pacific to readdress the debate. Our simulations show that the paleoclimate records are not reconcilable with the established concept of Laurentide-Eurasia-only ice sheets. On the contrary, a Beringian ice sheet over Northeast Siberia-Beringia causes feedbacks between atmosphere and ocean, the result of which well explains the climate records from around the North Pacific during the past four glacial-interglacial cycles. Our ice-climate modelling and synthesis of paleoclimate records from around the North Pacific argue that the Beringian ice sheet waxed and waned rapidly in the past four glacial-interglacial cycles and accounted for ~10-25 m ice-equivalent sea-level change during its peak glacials. The simulated Beringian ice sheet agrees reasonably with the direct glacial and climate evidence from Northeast Siberia-Beringia, and reconciles the paleoclimate records from around the North Pacific. With the Beringian ice sheet involved, the pattern of past NH ice sheet evolution is more complex than previously thought, in particular prior to the LGM.</p>

A modelling perspective of North Pacific Intermediate water in the future

2020 ◽  
Author(s):  
Xun Gong ◽  
Lars Ackermann ◽  
Gerrit Lohmann
Keyword(s):  
Pacific Ocean ◽  
North Pacific ◽  
Carbon Sink ◽  
North Pacific Ocean ◽  
Intermediate Water ◽  
North Pacific Intermediate Water ◽  
The North ◽  
The Future ◽  
Near Future ◽  
The North Pacific

<p>North Pacific Intermediate water (NPIW) is a dominant water mass controlling ~400-1200m depth North Pacific Ocean, characterized by its low salinities and relatively lower temperatures. In the modern climate, the interplay between NPIW-related physical and biogeochemical processes among seasons determines annual-mean budget and efficiency of carbon sink into the North Pacific Ocean. Thus, to understand the NPIW physics is key to project roles of the North Pacific Ocean in changing Earth climate and carbon systems in the future. In this study, we provide a modelling view of the NPIW history since Yr 1850 (historical experiment) and its projection to near future (IPCC-defined RCP 4.2 and 8.5 experiments until Yr 2100), using new-generation Alfred Wegener Institute Earth System Model (AWI-ESM). Our results suggest an important role of regional hydroclimate feedback over the NW Pacific and Sea of Okhotsk in determining the NPIW from recent past to near future.</p>

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