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>

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 Rapid shift and millennial-scale variations in Holocene North Pacific Intermediate Water ventilation

2018 ◽  
Vol 115 (21) ◽  
pp. 5365-5370 ◽  
Author(s):  
Lester Lembke-Jene ◽  
Ralf Tiedemann ◽  
Dirk Nürnberg ◽  
Xun Gong ◽  
Gerrit Lohmann
Keyword(s):  
North Pacific ◽  
World Ocean ◽  
Future Climate Change ◽  
Nutrient Concentrations ◽  
Intermediate Water ◽  
Okhotsk Sea ◽  
North Pacific Intermediate Water ◽  
The North ◽  
The Pacific ◽  
Millennial Scale

The Pacific hosts the largest oxygen minimum zones (OMZs) in the world ocean, which are thought to intensify and expand under future climate change, with significant consequences for marine ecosystems, biogeochemical cycles, and fisheries. At present, no deep ventilation occurs in the North Pacific due to a persistent halocline, but relatively better-oxygenated subsurface North Pacific Intermediate Water (NPIW) mitigates OMZ development in lower latitudes. Over the past decades, instrumental data show decreasing oxygenation in NPIW; however, long-term variations in middepth ventilation are potentially large, obscuring anthropogenic influences against millennial-scale natural background shifts. Here, we use paleoceanographic proxy evidence from the Okhotsk Sea, the foremost North Pacific ventilation region, to show that its modern oxygenated pattern is a relatively recent feature, with little to no ventilation before six thousand years ago, constituting an apparent Early–Middle Holocene (EMH) threshold or “tipping point.” Complementary paleomodeling results likewise indicate a warmer, saltier EMH NPIW, different from its modern conditions. During the EMH, the Okhotsk Sea switched from a modern oxygenation source to a sink, through a combination of sea ice loss, higher water temperatures, and remineralization rates, inhibiting ventilation. We estimate a strongly decreased EMH NPIW oxygenation of ∼30 to 50%, and increased middepth Pacific nutrient concentrations and carbon storage. Our results (i) imply that under past or future warmer-than-present conditions, oceanic biogeochemical feedback mechanisms may change or even switch direction, and (ii) provide constraints on the high-latitude North Pacific’s influence on mesopelagic ventilation dynamics, with consequences for large oceanic regions.

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 Distributions of mixed layer properties in North Pacific water mass formation areas: comparison of Argo floats and World Ocean Atlas 2001

Ocean Science ◽  
2006 ◽  
Vol 2 (1) ◽  
pp. 61-70 ◽  
Author(s):  
F. M. Bingham ◽  
T. Suga
Keyword(s):  
Mixed Layer ◽  
North Pacific ◽  
World Ocean ◽  
Water Masses ◽  
Mode Water ◽  
The North ◽  
Central Mode Water ◽  
Central Mode ◽  
World Ocean Atlas ◽  
The North Pacific

Abstract. Winter mixed layer characteristics in the North Pacific Ocean are examined and compared between Argo floats in 2006 and the World Ocean Atlas 2001 (WOA01) climatology for a series of named water masses, North Pacific Tropical Water (NPTW), Eastern Subtropical Mode Water (ESTMW), North Pacific Subtropical Mode Water (NPSTMW), Light Central Mode Water (LCMW) and Dense Central Mode Water (DCMW). The WOA01 is found to be in good agreement with the Argo data in terms of water mass volumes, average temperature-salinity (T-S) properties, and outcrop areas. The exception to this conclusion is for the central mode waters, DCMW and LCMW, whose outcropping is shown to be much more intermittent than is apparent in the WOA01 and whose T-S properties vary from what is shown in the WOA01. Distributions of mixed layer T-S properties measured by floats are examined within the outcropping areas defined by the WOA01 and show some shifting of T-S characteristics within the confines of the named water masses. In 2006, all the water masses were warmer than climatology on average, with a magnitude of about 0.5°C. The NPTW, NPSTMW and LCMW were saltier than climatology and the ESTMW and DCMW fresher, with magnitudes of about 0.05. In order to put these results into context, differences between Argo and WOA01 were examined over the North Pacific between 20 and 45° N. A large-scsale warming and freshening is seen throughout this area, except for the western North Pacific, where results were more mixed.

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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