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1. The California Undercurrent as a Source of Upwelled Waters in a Coastal Filament

   https://doi.org/10.1029/2020JC016602  

   Zaba, Katherine D. ; Franks, Peter J. S. ; Ohman, Mark D. ( February 2021 , Journal of Geophysical Research: Oceans)

   In the California Current System, cross‐shore transport of upwelled, nutrient‐rich waters from the coastal margin to the open ocean can occur within intermittent, submesoscale‐to‐mesoscale features such as filaments. Time‐varying spatial gradients within filaments affect net cross‐shore fluxes of physical, biological, and chemical tracers but require high‐resolution measurements to accurately estimate. In June 2017, theCalifornia Current EcosystemLong Term Ecological Research program process cruise (P1706) conducted repeat sections by an autonomousSprayglider and a towed SeaSoar to investigate the role of one such coastal upwelling feature, the Morro Bay filament, which was characterized by enhanced cross‐filament gradients (both physical and biological) and an along‐filament jet. Within the jet, speeds were up to 0.78 m/s and the offshore transport was 1.5 Sverdrups (3.8 Sverdrups) in the upper 100 m (500 m). A climatological data product from the sustained California Underwater Glider Network provided necessary information for water mass differentiation. The analysis revealed that the cold, salty side of the filament carried recently upwelled California Undercurrent water and corresponded to higher chlorophyll‐afluorescence than the warm, fresh side, which carried California Current water. Thus, there was a convergence of heterogeneous water masses within the core of the filament’s offshore‐flowing jet. These water masses have different geographic origins and thermohaline characteristics, which has implications for filament‐related cross‐shore fluxes and submesoscale‐to‐mesoscale biological community structure gradients.

    

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2. Long Island Sound temperature variability and its associations with the ridge–trough dipole and tropical modes of sea surface temperature variability

   https://doi.org/10.5194/os-15-161-2019  

   Schulte, Justin A. ; Lee, Sukyoung ( January 2019 , Ocean Science)

   Abstract. Possible mechanisms behind the longevity of intense Long IslandSound (LIS) water temperature events are examined using an event-basedapproach. By decomposing an LIS surface water temperature time series intonegative and positive events, it is revealed that the most intense LIS watertemperature event in the 1979–2013 period occurred around 2012, coincidingwith the 2012 ocean heat wave across the Mid-Atlantic Bight. The LIS eventsare related to a ridge–trough dipole pattern whose strength and evolution canbe determined using a dipole index. The dipole index was shown to be stronglycorrelated with LIS water temperature anomalies, explaining close to 64 %of cool-season LIS water temperature variability. Consistently, a majordipole pattern event coincided with the intense 2012 LIS warm event. Acomposite analysis revealed that long-lived intense LIS water temperatureevents are associated with tropical sea surface temperature (SST) patterns.The onset and mature phases of LIS cold events were shown to coincide withcentral Pacific El Niño events, whereas the termination of LIS coldevents was shown to possibly coincide with canonical El Niño events or ElNiño events that are a mixture of eastern and central Pacific El Niñoflavors. The mature phase of LIS warm events was shown to be associated withnegative SST anomalies across the central equatorial Pacific, though theresults were not found to be robust. The dipole pattern was also shown to berelated to tropical SST patterns, and fluctuations in central Pacific SSTanomalies were shown to evolve coherently with the dipole pattern and thestrongly related East Pacific–North Pacific pattern on decadal timescales.The results from this study have important implications for seasonal anddecadal prediction of the LIS thermal system. 

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3. Phosphate Scavenging During Lava‐Seawater Interaction Offshore of Kīlauea Volcano, Hawaii

   https://doi.org/10.1029/2021GC009754  

   Foreman, Rhea K. ; Björkman, Karin M. ; Funkey, Carolina P. ; Hawco, Nicholas J. ; Wilson, Samuel T. ; Rohrer, Tully ; White, Angelicque E. ; John, Seth G. ; Karl, David M. ( July 2021 , Geochemistry, Geophysics, Geosystems)

   The 2018, subaerial eruption of Kīlauea volcano, Hawaii, resulted in a 5‐km‐long stretch of coastline that actively drained lava into the ocean. Nutrients were added to the surrounding ocean through the dissolution of basaltic rock and thermal upwelling of deep water, thereby fueling a large phytoplankton bloom. Lava‐impacted, surface seawater had high suspended particle loads, and concentrations of chlorophyll, silicic acid, phosphate (P_i), nitrate, and iron that were elevated up to 12, 36, 5, 960, and 1,400 times, respectively, above the background oligotrophic levels. Widespread precipitation of iron oxyhydroxides (Fe_ox) led to extensive scavenging of the dissolved P_ipool, similar to what occurs along mid‐ocean ridge hydrothermal systems. This scavenging transformed a “fertilization” event into a P_isink near the coast of the ocean entry; however, nutrient data from outside the bloom suggest that P_icould also desorb from the Fe_oxas it is dispersed into the open ocean. From lava quench experiments, we estimate that the hydration state of the Fe_oxprecipitate (H₂O/Fe) was 5.2–5.7, and that the equilibrium partition coefficient of P_iinto Fe_ox(solid/liquid) was 10⁶. In addition,³³P_iradiotracer incubations were used to differentiate between biotic and abiotic uptake of P_iat Kīlauea's ocean entry. These findings are important for understanding modern‐day volcanic fertilization events, modeling nutrient dynamics during major events in Earth history (such as oxygenation of the atmosphere and the formation of large igneous provinces), and predicting the marine response to greater continental weathering in a warming climate.

    

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4. Eddy Vertical Structure and Variability: Deepglider Observations in the North Atlantic

   https://doi.org/10.1175/JPO-D-21-0068.1  

   Steinberg, Jacob M. ; Eriksen, Charles C. ( June 2022 , Journal of Physical Oceanography)

   Abstract Hundreds of full-depth temperature and salinity profiles collected by Deepglider autonomous underwater vehicles (AUVs) in the North Atlantic reveal robust signals in eddy isopycnal vertical displacement and horizontal current throughout the entire water column. In separate glider missions southeast of Bermuda, subsurface-intensified cold, fresh coherent vortices were observed with velocities exceeding 20 cm s −1 at depths greater than 1000 m. With vertical resolution on the order of 20 m or less, these full-depth glider slant profiles newly permit estimation of scaled vertical wavenumber spectra from the barotropic through the 40th baroclinic mode. Geostrophic turbulence theory predictions of spectral slopes associated with the forward enstrophy cascade and proportional to inverse wavenumber cubed generally agree with glider-derived quasi-universal spectra of potential and kinetic energy found at a variety of locations distinguished by a wide range of mean surface eddy kinetic energy. Water-column average spectral estimates merge at high vertical mode number to established descriptions of internal wave spectra. Among glider mission sites, geographic and seasonal variability implicate bottom drag as a mechanism for dissipation, but also the need for more persistent sampling of the deep ocean. Significance Statement Relative to upper-ocean measurements of temperature, salinity, and velocity, deep ocean measurements (below 2000 m) are fewer in number and more difficult to collect. Deep measurements are needed, however, to explore the nature of deep ocean circulation contributing to the global redistribution of heat and to determine how upper-ocean behavior impacts or drives deep motions. Understanding of geographic and temporal variability in vertical structures of currents and eddies enables improved description of energy pathways in the ocean driven by turbulent interactions. In this study, we use newly developed autonomous underwater vehicles, capable of diving to the seafloor and back on a near daily basis, to collect high-resolution full ocean depth measurements at various locations in the North Atlantic. These measurements reveal connections between surface and deep motions, and importantly show their time evolution. Results of analyzing these vertical structures reveal the deep ocean to regularly “feel” events in the upper ocean and permit new comparisons to deep motions in climate models. 

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5. Dynamics of the Pacific Antarctic Circumpolar Current

   https://doi.org/10.14379/iodp.proc.383.2021  

   Lamy, F. ; Winckler, G. ; Alvarez Zarikian, C.A. ( July 2021 , Proceedings of the International Ocean Discovery Program)

   null (Ed.)

   The Antarctic Circumpolar Current (ACC), the world’s strongest zonal current system, connects all three major ocean basins of the global ocean and therefore integrates and responds to global climate variability. Its flow is largely driven by strong westerly winds and is constricted to its narrowest extent in the Drake Passage. Fresh and cold Pacific surface and intermediate water flowing through the Drake Passage (cold-water route) and warm Indian Ocean water masses flowing through the Agulhas region (warm-water route) are critical for the South Atlantic contribution to Meridional Overturning Circulation changes. Furthermore, physical and biological processes associated with the ACC affect the strength of the ocean carbon pump and therefore are critical to feedbacks linking atmospheric CO2 concentrations, ocean circulation, and climate/cryosphere on a global scale. In contrast to the Atlantic and Indian sectors of the ACC, and with the exception of drill cores from the Antarctic continental margin and off New Zealand, there are no deep-sea drilling paleoceanographic records from the Pacific sector of the ACC. To advance our understanding of Miocene to Holocene atmosphere-ocean-cryosphere dynamics in the Pacific and their implications for regional and global climate and atmospheric CO2, International Ocean Discovery Program Expedition 383 recovered sedimentary sequences at (1) three sites in the central South Pacific (CSP) (U1539, U1540, and U1541), (2) two sites at the Chilean margin (U1542 and U1544), and (3) one site from the pelagic eastern South Pacific (U1543) close to the entrance to the Drake Passage. Because of persistently stormy conditions and the resulting bad weather avoidance, we were not successful in recovering the originally planned Proposed Site CSP-3A in the Polar Frontal Zone of the CSP. The drilled sediments at Sites U1541 and U1543 reach back to the late Miocene, and those at Site U1540 reach back to the early Pliocene. High sedimentation rate sequences reaching back to the early Pleistocene (Site U1539) and the late Pleistocene (Sites U1542 and U1544) were recovered in both the CSP and at the Chilean margin. Taken together, the sites represent a depth transect from ~1100 m at Chilean margin Site U1542 to ~4070 m at CSP Site U1539 and allow investigation of changes in the vertical structure of the ACC, a key issue for understanding the role of the Southern Ocean in the global carbon cycle. The sites are located at latitudes and water depths where sediments will allow the application of a wide range of siliciclastic-, carbonate-, and opal-based proxies to address our objectives of reconstructing, with unprecedented stratigraphic detail, surface to deep-ocean variations and their relation to atmosphere and cryosphere changes. 

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