Changes in mixed layer depth and spring bloom in the Kuroshio extension under global warming

AbstractThe decadal to multidecadal mixed layer variability is investigated in a region south of the Kuroshio Extension (130°E–180°, 25°–35°N), an area where the North Pacific subtropical mode water forms, during 1948–2012. By analyzing the mixed layer heat budget with different observational and reanalysis data, here we show that the decadal to multidecadal variability of the mixed layer temperature and mixed layer depth is covaried with the Atlantic multidecadal oscillation (AMO), instead of the Pacific decadal oscillation (PDO). The mixed layer temperature has strong decadal to multidecadal variability, being warm before 1970 and after 1990 (AMO positive phase) and cold during 1970–90 (AMO negative phase), and so does the mixed layer depth. The dominant process for the mixed layer temperature decadal to multidecadal variability is the Ekman advection, which is controlled by the zonal wind changes related to the AMO. The net heat flux into the ocean surface Qnet acts as a damping term and it is mainly from the effect of latent heat flux and partially from sensible heat flux. While the wind as well as mixed layer temperature decadal changes related to the PDO are weak in the western Pacific Ocean. Our finding proposes the possible influence of the AMO on the northwestern Pacific Ocean mixed layer variability, and could be a potential predictor for the decadal to multidecadal climate variability in the western Pacific Ocean.

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Decadal Variation in Winter Mixed Layer Depth South of the Kuroshio Extension and Its Influence on Winter Mixed Layer Temperature

Journal of Climate ◽

10.1175/jcli-d-15-0206.1 ◽

2016 ◽

Vol 29 (3) ◽

pp. 1237-1252 ◽

Cited By ~ 19

Author(s):

Shusaku Sugimoto ◽

Shin’ichiro Kako

Keyword(s):

Mixed Layer ◽

North Pacific ◽

Kuroshio Extension ◽

Mixed Layer Depth ◽

Positive Anomaly ◽

Surface Cooling ◽

Layer Depth ◽

Mixed Layer Temperature ◽

Winter Mixed Layer ◽

The Kuroshio

Abstract The long-term behavior of the wintertime mixed layer depth (MLD) and mixed layer temperature (MLT) are investigated in a region south of the Kuroshio Extension (KE) (30°–37°N, 141°–155°E), an area of the North Pacific subtropical gyre where the deepest MLD occurs, using historical temperature profiles of 1968–2014. Both the MLD and MLT in March have low-frequency variations, which show significant decadal (~10 yr) variations after the late 1980s. Observational data and simulation outputs from a one-dimensional turbulent closure model reveal that surface cooling is the main control on winter MLD in the late 1970s and 1980s, whereas there is a change in the strength of subsurface stratification is the main control after ~1990. In the latter period, a weak (strong) subsurface stratification is caused by a straight path (convoluted path) of the KE and by a deepening (shallowing) of the main thermocline depth due to oceanic Rossby waves formed as a result of positive (negative) anomalies of wind stress curl associated with a southward (northward) movement of the Aleutian low in the central North Pacific. During deeper (shallower) periods of winter MLD, the strong (weak) vertical entrainment process, resulting from a rapid (slow) deepening of the mixed layer (ML) in January and February, forms a negative (positive) anomaly of temperature tendency. Consequently, the decadal variations in wintertime MLT are formed.

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Japanese sardine (Sardinops melanostictus) mortality in relation to the winter mixed layer depth in the Kuroshio Extension region

Fisheries Oceanography ◽

10.1111/j.1365-2419.2008.00487.x ◽

2008 ◽

Vol 17 (5) ◽

pp. 411-420 ◽

Cited By ~ 22

Author(s):

HARUKA NISHIKAWA ◽

ICHIRO YASUDA

Keyword(s):

Mixed Layer ◽

Kuroshio Extension ◽

Mixed Layer Depth ◽

Layer Depth ◽

Japanese Sardine ◽

Winter Mixed Layer ◽

The Kuroshio ◽

Kuroshio Extension Region

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Winter mixed layer depth and spring bloom along the Kuroshio front: implications for the Japanese sardine stock

Marine Ecology Progress Series ◽

10.3354/meps10201 ◽

2013 ◽

Vol 487 ◽

pp. 217-229 ◽

Cited By ~ 20

Author(s):

H Nishikawa ◽

I Yasuda ◽

K Komatsu ◽

H Sasaki ◽

Y Sasai ◽

...

Keyword(s):

Mixed Layer ◽

Spring Bloom ◽

Mixed Layer Depth ◽

Layer Depth ◽

Japanese Sardine ◽

Winter Mixed Layer ◽

Kuroshio Front ◽

The Kuroshio

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Winter Extreme Mixed Layer Depth South of the Kuroshio Extension

Journal of Climate ◽

10.1175/jcli-d-20-0119.1 ◽

2020 ◽

Vol 33 (24) ◽

pp. 10419-10436

Author(s):

Jingjie Yu ◽

Bolan Gan ◽

Zhao Jing ◽

Lixin Wu

Keyword(s):

Heat Flux ◽

Mixed Layer ◽

Kuroshio Extension ◽

Mixed Layer Depth ◽

Surface Cooling ◽

Layer Depth ◽

Mode Water ◽

Surface Warming ◽

Mechanical Stirring ◽

The Kuroshio

AbstractChange in the extratropical wintertime-mean mixed layer has been widely studied, given its importance to both physical and biogeochemical processes. With a focus on the south of the Kuroshio Extension region where the mixed layer is deepest in March, this study shows that variation of the synoptic-scale extreme mixed layer depth (MLD) is a better precursor than the monthly mean (or nonextreme) MLD for change in the subtropical mode water formation in spring, based on the NCEP Climate Forecast System Reanalysis (1979–2010). It is found that the extreme MLD events are attributable to the accumulation of excessive surface cooling driven by the synoptic storms that characterize cold-air outbreaks. Particularly, the difference between the extreme and nonextreme MLD is primarily related to differences in the cumulative synoptic heat flux anomalies, while a change in the preconditioning upper-ocean stratification contributes almost equally to both cases. Relative contributions of oceanic and atmospheric forcing to the interannual variation of the extreme MLD are quantified using a bulk mixed layer model. Results show comparable contributions: the preconditioning stratification change accounts for ~44% of total variance of the extreme MLD, whereas the convective mixing by surface heat flux and the mechanical stirring by wind stress account for ~35% and ~13%, respectively. In addition, both the reanalysis and observational data reveal that the extreme and nonextreme MLD has been shallowed significantly during 1979–2010, which is accounted for by the strengthened stratification due to the enhanced ocean surface warming by the Kuroshio heat transport.

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Response of the mixed layer depth and subduction rate in the subtropical Northeast Pacific to global warming

Acta Oceanologica Sinica ◽

10.1007/s13131-021-1818-y ◽

2021 ◽

Author(s):

Ruibin Xia ◽

Bingrui Li ◽

Cheng Chen

Keyword(s):

Global Warming ◽

Mixed Layer ◽

Mixed Layer Depth ◽

Layer Depth ◽

Northeast Pacific ◽

Subduction Rate

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Response of the ocean mixed layer depth to global warming and its impact on primary production: a case for the North Pacific Ocean

ICES Journal of Marine Science ◽

10.1093/icesjms/fsr064 ◽

2011 ◽

Vol 68 (6) ◽

pp. 996-1007 ◽

Cited By ~ 25

Author(s):

Chan Joo Jang ◽

Jisoo Park ◽

Taewook Park ◽

Sinjae Yoo

Keyword(s):

Global Warming ◽

Pacific Ocean ◽

Primary Production ◽

Mixed Layer ◽

North Pacific ◽

North Pacific Ocean ◽

Mixed Layer Depth ◽

Layer Depth ◽

The North ◽

The North Pacific

Abstract Jang, C. J., Park, J., Park, T., and Yoo, S. 2011. Response of the ocean mixed layer depth to global warming and its impact on primary production: a case for the North Pacific Ocean. – ICES Journal of Marine Science, 68: 996–1007. This study investigates changes in the mixed layer depth (MLD) in the North Pacific Ocean in response to global warming and their impact on primary production by comparing outputs from 11 models of the coupled model intercomparison projects phase 3. The MLD in the 21st century decreases in most regions of the North Pacific, whereas the spatial pattern of the MLD is nearly unchanged. The overall shoaling results in part from intensified upper-ocean stratification caused by both surface warming and freshening. A significant MLD decrease (>30 m) is found in the Kuroshio extension (KE), which is predominantly driven by reduced surface cooling, caused by weakening of wind. Associated with the mixed layer shoaling in the KE, the primary production component resulting from seasonal vertical mixing will be reduced by 10.7–40.3% (ranges of medians from 11 models) via decreased nitrate fluxes from below it. Spring blooms in most models are projected to initiate earlier in the KE by 0–13 d (ranges of medians from 11 models). Despite the overall trends, the magnitude of changes in primary production and timing of spring blooms are quite different depending on models and latitudes.

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