Characteristics of marine heatwaves (MHWs) in the East Asian Marginal Seas (EAMS) were investigated using the daily Optimum Interpolation Sea Surface Temperature for 37 years (1982–2018), focusing on seasonal changes and regional differences. The summer MHWs occur 54% more frequently (2.7 events/decade) in a relatively wide area than in other seasons. The strong (up to 3.7 °C) and long-lasting (up to 38 days/event) winter MHWs are concentrated along the subpolar front (SPF) in the East/Japan Sea (EJS) where the MHWs are 20% longer (2.2 days/event) than in the Yellow and East China Seas (YECS). The summer MHWs are primarily driven by increased shortwave radiation associated with reduced cloud cover and latent cooling from the weakened wind over the western flank of developing subtropical highs. Driving mechanisms of the winter MHWs differ by region. The YECS MHWs occur mainly due to the atmospheric processes associated with weakening continental highs, while the EJS MHWs are largely driven by the northward shift of the SPF. Although large-scale atmospheric processes primarily drive the summer MHWs occurring in a wide area in the EAMS, our findings suggest that ocean processes can be major contributors to intensified MHW generation in limited areas, especially in winter.

The mixed layer depth (MLD) is generally estimated using in situ or model data. However, MLD analyses have limitations due to the sparse resolution of the observed data. Therefore, this study reconstructs three-dimensional (3D) ocean thermal structures using only satellite sea surface measurements for a higher spatial and longer temporal resolution than that of Argo and diagnoses the decadal variation of global MLD variability. To simulate the ocean thermal structures, the relationship between the ocean subsurface temperature and the sea surface fields was computed based on gridded Argo data. Based on this relationship, high spatial resolution and extended periods of satellite-derived altimeter, sea surface temperature (SST), and wind stress data were used to estimate the 3D ocean thermal structures with 0.25° spatial resolution and 26 standard depth levels (5–2000 m) for 24 years (1993–2016). Then, the MLD was calculated using a temperature threshold method (∆T = 0.2 °C) and correlated reasonably well (>0.9) with other MLD datasets. The extended 24-year data enabled us to analyze the decadal variability of the MLD. The global linear trend of the 24-year MLD is −0.110 m yr⁻¹; however, from 1998 to 2012, the linear trend is −0.003 m yr⁻¹ which is an order of magnitude smaller than that of other periods and corresponds to a global warming hiatus period. Via comparisons between the trends of the SST anomalies and the MLD anomalies, we tracked how the MLD trend changes in response to the global warming hiatus.

Anchovy (Engraulis japonicus), a commercially and biologically important fish species in Korean waters, is a small pelagic fish sensitive to environmental change. Future changes in its distribution in Korean waters with significant environmental change remain poorly understood. In this study, we examined the projected changes in the seasonal anchovy habitat in Korean waters in the 2050s under three representative concentration pathways (RCPs; RCP 2.6, RCP 4.5, and RCP 8.5) by using a maximum entropy model (MaxEnt). The MaxEnt was constructed by anchovy presence points and five environmental variables (sea surface temperature, sea surface salinity, sea surface current speed, mixed layer depth, and chlorophyll-a concentration) from 2000–2015. Future changes in the anchovy habitat in Korean waters showed variation with seasonality: in the 2050s, during winter and spring, the anchovy habitat area is projected to increase by 19.4–38.4%, while in summer and fall, the habitat area is projected to decrease by up to 19.4% compared with the historical period (2000–2015) under the three different RCPs. A substantial decline (16.5–60.8%) is expected in summer in the East China Sea and the Yellow Sea—main spawning habitat. This considerable decrease in the spawning habitat may contribute to a decline in the anchovy biomass, relocation of the spawning area, and changes in the reproduction timing in Korean waters. Our findings suggest that seasonal variation of the anchovy habitat should be considered to ensure effective future management strategies for the effect of climate change on fisheries resources, particularly for environmentally sensitive species, such as anchovy.

The Seychelles-Chagos Thermocline Ridge (SCTR, 5°S-10°S, 50°E-80°E) is a unique open-ocean upwelling region in the southwestern Indian Ocean. Due to the negative wind stress curl between the equatorial westerlies and southeasterly trade winds, SCTR is known as a strong upwelling region with high biological productivity, providing a primary fishing zone for the surrounding countries. Given its importance in shaping the variability of the Indian Ocean climate by understanding the sea-air interaction and its dynamics, the simulation of SCTR is evaluated using outputs from the Coupled Model Intercomparison Project Phase Sixth (CMIP6). Compared to observations, 23 out of 27 CMIP6 models tend to simulate considerably deeper SCTR thermocline depth (defined as the 20°C isotherm depth (D20))– a common bias in climate models. The deep bias is related to the easterly wind bias in the equatorial to southern Indian Ocean, which is prominent in boreal summer and fall. This easterly wind bias produces a weak annual mean Ekman pumping, especially in the boreal fall. Throughout the year, the observed Ekman pumping is positive and is driven by two components: the curl term, is associated with the wind stress curl, leads to upwelling during boreal summer to fall; the beta term, is linked to planetary beta and zonal wind stress, contributes to downwelling during boreal spring to fall. However, the easterly wind bias in the CMIP6 increases both the positive curl and negative beta terms. The beta term bias offsets the curl term bias and reduces the upwelling velocity. Furthermore, the easterly wind bias is likely caused by the reduced east-west sea surface temperature (SST) difference associated with a pronounced warm bias in the western equatorial Indian Ocean, accompanied by the east-west mean sea level pressure gradient over the Indian Ocean. Furthermore, this study finds local wind-induced Ekman pumping to be a more dominant factor in thermocline depth bias than Rossby waves, despite CMIP6 models replicating Rossby wave propagation. This study highlights the importance of the beta term in the Ekman pumping simulation. Thus, reducing the boreal summer-to-fall easterly wind bias over the Indian Ocean region may improve the thermocline depth simulation over the SCTR region.

Kim, Y.S.; Jang, C.J.; Jeong, J.-Y., and Shim J.-S., 2018. Daily to seasonal variability of the mixed layer depth in the central Yellow Sea: Effects of atmospheric forcing. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 576–580. Coconut Creek (Florida), ISSN 0749-0208. Daily to seasonal variability of the mixed layer depth (MLD) was investigated based on the CTD mooring time series during the April to October 2015 period, taken from the Ongjin Socheongcho Ocean Research Station in the central Yellow Sea. The time evolution of the seasonal MLD was characterized by three distinct phases: fully-mixed (deep) phase by late April, quasi-stable (shallow) phase from late April to late July, and gradual deepening phase thereafter. During the first phase, the entire water column was occupied by cold bottom waters, which seemed to impede the change of the MLD a...

Information about wind variations and future wind conditions is essential for a monsoon domain such as the Northwest Pacific (NWP) region. This study utilizes 10 Generalized Circulation Models (GCM) from CMIP6 to evaluate near-future wind changes in the NWP under various climate warming scenarios. Evaluation against the ERA5 reanalysis dataset for the historical period 1985–2014 reveals a relatively small error with an average of no more than 1 m/s, particularly in the East Asian Marginal Seas (EAMS). Future projections (2026–2050) indicate intensified winds, with a 5–8% increase in the summer season in the EAMS, such as the Yellow Sea, East Sea, and East China Sea, while slight decreases are observed in the winter period. Climate mode influences show that winter El Niño tends to decrease wind speeds in the southern study domain, while intensifying winds are observed in the northern part, particularly under SSP5-8.5. Conversely, summer El Niño induces higher positive anomalous wind speeds in the EAMS, observed in SSP2-4.5. These conditions are likely linked to El Niño-induced SST anomalies. For the application of CMIP6 surface winds, the findings are essential for further investigations focusing on the oceanic consequences of anticipated wind changes such as the ocean wave climate, which can be studied through model simulations.