Remote effects of mixed layer development on ocean acidification in the subsurface layers of the North Pacific

Abstract Recent evidence shows that the North Pacific subtropical gyre, the Kuroshio Extension (KE) and Oyashio Extension (OE) fronts have moved poleward in the past few decades. However, changes of the North Pacific Subtropical Fronts (STFs), anchored by the North Pacific subtropical countercurrent in the southern subtropical gyre, remain to be quantified. By synthesizing observations, reanalysis, and eddy-resolving ocean hindcasts, we show that the STFs, especially their eastern part, weakened (20%±5%) and moved poleward (1.6°±0.4°) from 1980 to 2018. Changes of the STFs are modified by mode waters to the north. We find that the central mode water (CMW) (180°-160°W) shows most significant weakening (18%±7%) and poleward shifting (2.4°±0.9°) trends, while the eastern part of the subtropical mode water (STMW) (160°E-180°) has similar but moderate changes (10% ± 8%; 0.9°±0.4°). Trends of the western part of the STMW (140°E-160°E) are not evident. The weakening and poleward shifting of mode waters and STFs are enhanced to the east and are mainly associated with changes of the northern deep mixed layers and outcrop lines—which have a growing northward shift as they elongate to the east. The eastern deep mixed layer shows the largest shallowing trend, where the subduction rate also decreases the most. The mixed layer and outcrop line changes are strongly coupled with the northward migration of the North Pacific subtropical gyre and the KE/OE jets as a result of the poleward expanded Hadley cell, indicating that the KE/OE fronts, mode waters, and STFs change as a whole system.

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Quantifying the influence of CO<sub>2</sub> seasonality on future ocean acidification

Biogeosciences Discussions ◽

10.5194/bgd-12-5907-2015 ◽

2015 ◽

Vol 12 (8) ◽

pp. 5907-5940

Author(s):

T. P. Sasse ◽

B. I. McNeil ◽

R. J. Matear ◽

A. Lenton

Keyword(s):

Ocean Acidification ◽

North Pacific ◽

Dissolved Inorganic Carbon ◽

Marine Ecosystem ◽

Global Ocean ◽

Saturation State ◽

The North ◽

Data Limitations ◽

The Future ◽

The North Pacific

Abstract. Ocean acidification is a predictable consequence of rising atmospheric carbon dioxide (CO2), and is highly likely to impact the entire marine ecosystem – from plankton at the base to fish at the top. Factors which are expected to be impacted include reproductive health, organism growth and species composition and distribution. Predicting when critical threshold values will be reached is crucial for projecting the future health of marine ecosystems and for marine resources planning and management. The impacts of ocean acidification will be first felt at the seasonal scale, however our understanding how seasonal variability will influence rates of future ocean acidification remains poorly constrained due to current model and data limitations. To address this issue, we first quantified the seasonal cycle of aragonite saturation state utilizing new data-based estimates of global ocean surface dissolved inorganic carbon and alkalinity. This seasonality was then combined with earth system model projections under different emissions scenarios (RCPs 2.6, 4.5 and 8.5) to provide new insights into future aragonite under-saturation onset. Under a high emissions scenario (RCP 8.5), our results suggest accounting for seasonality will bring forward the initial onset of month-long under-saturation by 17 years compared to annual-mean estimates, with differences extending up to 35 ± 17 years in the North Pacific due to strong regional seasonality. Our results also show large-scale under-saturation once atmospheric CO2 reaches 486 ppm in the North Pacific and 511 ppm in the Southern Ocean independent of emission scenario. Our results suggest that accounting for seasonality is critical to projecting the future impacts of ocean acidification on the marine environment.

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Ocean acidification from 1997 to 2011 in the subarctic western North Pacific Ocean

Biogeosciences Discussions ◽

10.5194/bgd-10-8283-2013 ◽

2013 ◽

Vol 10 (5) ◽

pp. 8283-8311 ◽

Cited By ~ 1

Author(s):

M. Wakita ◽

S. Watanabe ◽

M. Honda ◽

A. Nagano ◽

K. Kimoto ◽

...

Keyword(s):

Ocean Acidification ◽

Mixed Layer ◽

North Pacific ◽

Dissolved Inorganic Carbon ◽

North Pacific Ocean ◽

Total Alkalinity ◽

Co2 Uptake ◽

The North ◽

Western Subarctic Gyre ◽

Calcite Saturation

Abstract. Rising atmospheric CO2 contents have led to greater CO2 uptake by the oceans, lowering both pH due to increasing hydrogen ions and CaCO3 saturation states due to declining carbonate ion (CO32−). Here, we used previously compiled data sets and new data collected in 2010 and 2011 to investigate ocean acidification of the North Pacific western subarctic gyre. In winter, the western subarctic gyre is a source of CO2 to the atmosphere because of convective mixing of deep waters rich in dissolved inorganic carbon (DIC). We calculated pH in winter mixed layer from DIC and total alkalinity (TA), and found that it decreased at the rate of −0.001 ± 0.0004 yr−1 from 1997 to 2011. This decrease rate is slower than that expected under condition of seawater/atmosphere equilibration, and it is also slower than the rate in the subtropical regions (−0.002 yr−1). The slow rate is caused by a reduction of CO2 emission in winter due to an increase in TA. Below the mixed layer, the calcite saturation horizon (~185 m depth) shoaled at the rate of 2.9 ± 0.9 m yr−1 as the result of the declining CO32− concentration (−0.03 ± 0.01 μmol k−1yr−1). Between 200 m and 300 m depth, pH decline during the study period (−0.0051 ± 0.0010 yr−1) was larger than ever reported in the open North Pacific. This enhanced acidification rate below the calcite saturation horizon reflected not only the uptake of anthropogenic CO2 but also the increase in the decomposition of organic matter evaluated from the increase in AOU, which suggests that the dissolution of CaCO3 particles increased.

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Heat and salt budgets of the mixed layer around the Subarctic Front of the North Pacific Ocean

“Hot Spots” in the Climate System ◽

10.1007/978-4-431-56053-1_4 ◽

2016 ◽

pp. 59-72

Author(s):

Vincent Faure ◽

Yoshimi Kawai

Keyword(s):

Pacific Ocean ◽

Mixed Layer ◽

North Pacific ◽

North Pacific Ocean ◽

The North ◽

Subarctic Front ◽

The North Pacific

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

Ocean Science ◽

10.5194/os-2-61-2006 ◽

2006 ◽

Vol 2 (1) ◽

pp. 61-70 ◽

Cited By ~ 13

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.

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Interannual-decadal variability of wintertime mixed layer depths in the North Pacific detected by an ensemble of ocean syntheses

Climate Dynamics ◽

10.1007/s00382-015-2762-3 ◽

2015 ◽

Vol 49 (3) ◽

pp. 891-907 ◽

Cited By ~ 13

Author(s):

Takahiro Toyoda ◽

Yosuke Fujii ◽

Tsurane Kuragano ◽

Naohiro Kosugi ◽

Daisuke Sasano ◽

...

Keyword(s):

Mixed Layer ◽

North Pacific ◽

Decadal Variability ◽

The North ◽

The North Pacific

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The North Pacific Climatology of Winter Mixed Layer and Mode Waters

Journal of Physical Oceanography ◽

10.1175/1520-0485(2004)034<0003:tnpcow>2.0.co;2 ◽

2004 ◽

Vol 34 (1) ◽

pp. 3-22 ◽

Cited By ~ 156

Author(s):

Toshio Suga ◽

Kazunori Motoki ◽

Yoshikazu Aoki ◽

Alison M. Macdonald

Keyword(s):

Mixed Layer ◽

North Pacific ◽

Mode Waters ◽

The North ◽

Winter Mixed Layer ◽

The North Pacific

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Role of North Pacific Mixed Layer in the Response of SST Annual Cycle to Global Warming

Journal of Climate ◽

10.1175/jcli-d-14-00349.1 ◽

2015 ◽

Vol 28 (23) ◽

pp. 9451-9458 ◽

Cited By ~ 3

Author(s):

Changlin Chen ◽

Guihua Wang

Keyword(s):

Global Warming ◽

Mixed Layer ◽

Annual Cycle ◽

North Pacific ◽

North Pacific Ocean ◽

Mixed Layer Depth ◽

Ecological Impacts ◽

Global Ocean ◽

The North ◽

The North Pacific

Abstract The annual cycle of sea surface temperature (SST) in the North Pacific Ocean is examined in terms of its response to global warming based on climate model simulations from phase 5 of the Coupled Model Intercomparison Project (CMIP5). As the global ocean warms up, the SST in the North Pacific generally tends to increase and the warming is greater in summer than in winter, leading to a significant intensification of SST annual cycle. The mixed layer temperature equation is used to examine the mechanism of this intensification. Results show that the decrease of mixed layer depth (MLD) in summer is the main reason behind the intensification of SST annual cycle. Because the MLD in summer is much shallower than that in winter, the incoming net heat flux is trapped in a thinner surface layer in summer, causing a warmer summer SST and the amplification of SST annual cycle. The change of the SST annual cycle in the North Pacific may have profound ecological impacts.

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