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Cover page for Santos et al 2026 - Antarctic Bottom Water contraction drives abyssal ocean warming along SAMBA-West line (34.5°S) in the Argentine basin

Antarctic Bottom Water contraction drives abyssal ocean warming along SAMBA-West line (34.5°S) in the Argentine basin

Santos, D. M. C., T. C. Bilo, et al.

We present an updated assessment of abyssal temperature trends in the Argentine Basin using expanded hydrographic and moored observations from the SAMBA-West line. The study addresses two main questions: (1) What is the spatial distribution of the abyssal warming along the SAMBA-West line? (2) What mechanisms drive the observed changes? Using output from a high-resolution numerical simulation, we first characterize how the abyssal flow near 34.5°S relates to the broader basin-scale circulation, providing context for interpreting the observations. Within this framework, we find that SAMBA-West is situated within a dynamically complex junction of deep boundary currents and recirculation pathways in the northwestern portion of the Argentine Basin. A coherent, statistically significant warming trend is found across most of the array and vertically throughout the AABW layer, primarily due to its vertical contraction, likely reflecting reduced formation or export of the AABW.

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Cover page of McWhorter et al (2026) - Subsurface-biogeochemical-response-to-Hurricane-Idalia-within-a-cyclonic-eddy-and-river-plume-stratified-environment

Subsurface biogeochemical response to Hurricane Idalia within a cyclonic eddy and river plume–stratified environment

Jennifer K. McWhorter, Lev B. Looney, et al.

Satellite observations can reveal chlorophyll blooms in the wake of hurricane disturbances but their subsurface biogeochemical anomalies remain poorly described due to limited in situ observations. Here, we quantify the biogeochemical response across the ocean water column to Hurricane Idalia (2023) in the Gulf of America (also known as the Gulf of America). We compile observations across the eastern Gulf using satellite data and two autonomous platforms: a profiling Biogeochemical-Argo (BGC-Argo) float and saildrone. Prior to the formation of Hurricane Idalia, an anomalously large extension of the Mississippi River plume spanned much of the eastern Gulf, contributing low-salinity and high-chlorophyll conditions. Following Idalia’s passage, the saildrone observed surface chlorophyll increases in the river plume extension, while the BGC-Argo float observed subsurface nitrate depletion and oxygen enrichment. These changes occurred as the float measured background ocean conditions evolving from the edge of the Loop Current to a cyclonic eddy, influenced by the river plume extension. Increases in chlorophyll concentration, decreases in nitrate, and elevated dissolved oxygen levels suggested increased primary production. BGC-Argo float observations revealed enhanced upwelling below the surface layer (~22 m) that shoaled the nitracline, fueling the increase in subsurface primary production (20–50 m depth). Our study provides a glimpse on the surface and subsurface ocean-biogeochemical changes associated with the Hurricane Idalia passage, highlighting the importance of the background mesoscale seascape on shaping the phytoplankton response to hurricane-induced disturbances. The combination of observations underscores the value of continuous in situ monitoring to better understand hurricane-driven impacts on the full ocean water column and the impacts these dynamics have on the base of the marine food web.

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