The equatorial western‐central Pacific (WCP), characterized by low marine heatwave (MHW) occurrence and weak MHW intensity, is generally considered a refuge from MHWs. However, by integrating satellite observations with in situ measurements from BGC‐Argo floats and TAO/TRITON buoys, this study reveals that the WCP exhibits the strongest phytoplankton response to MHWs in the global ocean, with near‐surface chlorophyll concentration (CHL) declining by up to 50% per unit MHW intensity. This extreme response primarily arises from a concurrent reduction in both horizontal and vertical nutrient supply during MHWs. Eastward current anomaly inhibits zonal advection of nutrient‐rich water from the east, while enhanced salinity stratification and shoaled mixed layer hamper vertical nutrient supply. Contrary to the near‐surface, subsurface phytoplankton increase substantially during MHWs, mainly resulting from the improvement in nutrient and light conditions at depths below the shoaled mixed layer and near the base of the deepened euphotic layer. As the WCP hosts the world's most productive tuna fisheries and intense subsurface MHWs, our findings reveal a previously unrecognized ecological vulnerability with important implications for fishery management and carbon cycle in this vital marine system.
Weikang Zhan, Ying Zhang, Haigang Zhan et al.· Global Change Biology· 0 citations
Mesoscale eddies play a key role in regulating oceanic physical and biogeochemical environments. However, their influence on vertical oxygen distribution remains poorly constrained by observations. Using 32 years (1993–2024) of in situ oxygen observations from the Bermuda Atlantic Time‐series Study site combined with satellite‐tracked eddies, we show that eddy‐induced oxygen anomalies are substantially stronger in the mesopelagic than at the surface. Anticyclonic eddies deepen the subsurface oxygen minimum layer (OML) by ∼100 m and reduce its thickness by ∼30%, with increases of ∼3%–6% in mean and minimum oxygen. Cyclonic eddies induce a similar but weaker thinning, accompanied by an upward displacement of about 100 m. More than 80% of the variance is explained by isopycnal heaving, with additional contributions from biogeochemical processes. Our results underscore that both eddy types systematically alleviate low‐oxygen conditions within the OML, with important implications for subsurface oxygen habitat variability.
Peiyao Zhang, Weikang Zhan, Zhenting Mo et al.· Geophysical Research Letters· 0 citations
Mesoscale eddies in the Southern Ocean extend from the surface to the deep ocean and contribute to regional and global ocean heat budgets. However, sparse in situ observations have limited estimates of eddy meridional heat transport (EMHT) to the near surface, leaving deep-ocean processes poorly understood. Here we quantify deep eddy kinetic energy (EKE) and EMHT using Argo observations. We find that deep EMHT reaches at least the same order of magnitude as surface transport, despite deep EKE being only one-fifth of surface levels. Float observations and sensitivity experiments reveal that, relative to mean-flow transport alone, deep EMHT extends the meridional movement of subtropical warm waters towards Antarctica by over ten degrees of latitude. About 60% of this deep transport originates from the Indian Ocean sector. These findings provide observational evidence that mesoscale eddies can modulate deep Southern Ocean heat redistribution, with potential implications for Antarctic climate.
Tongya Liu, Xiaoming Zhai, Qingyou He et al.· Nature Communications· 0 citations
