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1. Propagation of North Atlantic Deep Water Anomalies

   https://doi.org/10.1175/JPO-D-18-0068.1  

   Nieves, David; Spall, Michael (August 2018, Journal of Physical Oceanography)
2. Transition paths of North Atlantic Deep Water

   https://doi.org/10.1175/JTECH-D-22-0022.1  

   Miron, P.; Beron-Vera, F. J.; Olascoaga, M. J. (May 2022, Journal of Atmospheric and Oceanic Technology)

   Abstract Recently introduced in oceanography to interpret the near surface circulation, Transition Path Theory ( TPT ) is a methodology that rigorously characterizes ensembles of trajectory pieces flowing out from a source last and into a target next, i.e., those that most productively contribute to transport. Here we use TPT to frame, in a statistically more robust fashion than earlier analysis, equatorward routes of North Atlantic Deep Water (NADW) in the subpolar North Atlantic. TPT is applied on all available RAFOS and Argo floats in the area by means of a discretization of the Lagrangian dynamics described by their trajectories. By considering floats at different depths, we investigate transition paths of NADW in its upper (UNADW) and lower (LNADW) layers. We find that the majority of UNADW transition paths sourced in the Labrador and southwestern Irminger Seas reach the western side of a target arranged zonally along the southern edge of the subpolar North Atlantic domain visited by the floats. This is accomplished in the form of a well-organized deep boundary current (DBC). LNADW transition paths sourced west of the Reykjanes Ridge reveal a similar pattern, while those sourced east of the ridge are found to hit the western side of the target via a DBC and also several other places along it in a less organized fashion, indicating southward flow along the eastern and western flanks of the Mid-Atlantic Ridge. Naked-eye inspection of trajectories suggest generally much more diffusive equatorward NADW routes. A source-independent dynamical decomposition of the flow domain into analogous backward-time basins of attraction, beyond the reach of direct inspection of trajectories, reveals a much wider influence of the western side of the target for UNADW than for LNADW. For UNADW, the average expected duration of the pathways from the Labrador and Irminger Seas was found to be of 2 to 3 years. For LNADW, the duration was found to be influenced by the Reykjanes Ridge, being as long as 8 years from the western side of the ridge and of about 3 years on average from its eastern side. 

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3. Atlantic-Pacific Asymmetry in Deep Water Formation

   https://doi.org/10.1146/annurev-earth-082517-010045  

   Ferreira, David; Cessi, Paola; Coxall, Helen K.; de Boer, Agatha; Dijkstra, Henk A.; Drijfhout, Sybren S.; Eldevik, Tor; Harnik, Nili; McManus, Jerry F.; Marshall, David P.; et al (May 2018, Annual Review of Earth and Planetary Sciences)

   While the Atlantic Ocean is ventilated by high-latitude deep water formation and exhibits a pole-to-pole overturning circulation, the Pacific Ocean does not. This asymmetric global overturning pattern has persisted for the past 2–3 million years, with evidence for different ventilation modes in the deeper past. In the current climate, the Atlantic-Pacific asymmetry occurs because the Atlantic is more saline, enabling deep convection. To what extent the salinity contrast between the two basins is dominated by atmospheric processes (larger net evaporation over the Atlantic) or oceanic processes (salinity transport into the Atlantic) remains an outstanding question. Numerical simulations have provided support for both mechanisms; observations of the present climate support a strong role for atmospheric processes as well as some modulation by oceanic processes. A major avenue for future work is the quantification of the various processes at play to identify which mechanisms are primary in different climate states. 

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4. Prokaryotic Life in the Deep Ocean's Water Column

   https://doi.org/10.1146/annurev-marine-032122-115655  

   Herndl, Gerhard J; Bayer, Barbara; Baltar, Federico; Reinthaler, Thomas (January 2023, Annual Review of Marine Science)

   The oceanic waters below a depth of 200 m represent, in terms of volume, the largest habitat of the biosphere, harboring approximately 70% of the prokaryotic biomass in the oceanic water column. These waters are characterized by low temperature, increasing hydrostatic pressure, and decreasing organic matter supply with depth. Recent methodological advances in microbial oceanography have refined our view of the ecology of prokaryotes in the dark ocean. Here, we review the ecology of prokaryotes of the dark ocean, present data on the biomass distribution and heterotrophic and chemolithoautotrophic prokaryotic production in the major oceanic basins, and highlight the phylogenetic and functional diversity of this part of the ocean. We describe the connectivity of surface and deep-water prokaryotes and the molecular adaptations of piezophilic prokaryotes to high hydrostatic pressure. We also highlight knowledge gaps in the ecology of the dark ocean's prokaryotes and their role in the biogeochemical cycles in the largest habitat of the biosphere. 

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5. TRACKING DEEP-WATER OXYGENATION CHANGES OFFSHORE SOUTHERN CALIFORNIA

   Duff, E.; Troxel, A.; Haygood, L.; Ford, T.; Burkett, A.; Reidinger, N. (March 2023, Geological Society of America South-Central Section)

   none. (Ed.)

   Upwelling systems on eastern boundaries of subtropical ocean basins are some of the most climatically dynamic regions of the oceans. Anthropogenic climate change has implications for these marine ecosystems, such as driving marine deoxygenation, driving ecosystem zonation, and driving the expansion of oxygen minimum zones (OMZ). There have been multiple studies evaluating drivers of marine oxygenation changes, yet there is still a need to understand surface processes and source waters influence on bottom-water oxygenation. The California continental margin is a well-studied upwelling system, where source water mixing of oxygen-rich subarctic waters to oxygen-poor subtropical waters is strongly influenced by the California Current, leading to one of the most primary production areas in the Pacific. Here we present data of redox sensitive trace metals to evaluate changes in the bottom water ventilation off the coast of Southern California due to climatic changes. Samples from several sediment cores were recovered via the RV Roger Revelle Expedition RV2206 during the summer of 2022. The sediment samples were digested applying a multi-acid digestion technique and analyzing together with pore water samples via inductively coupled plasma mass spectrometry. Interestingly, we observe a strong flux of specific heavy metals from the sediments into the overlying water column, likely impacting the benthic community and altering the primary metal-proxy signal at these sites with potential implications for the reconstruction of current ventilation through these geochemical and microfossil tracers. Overall, our preliminary results indicate fluctuations in the OMZ seaward expansion with implications for the oxygenation condition of the deeper water. 

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