Bering Sea deep circulation: Water properties and geopotential

Deep temperature and silicate data from the Bering Sea demonstrate patterns that are consistent and allow inference of near-bottom circulation. The cold source water enters Kamchatka Strait and mainly moves toward the southeast through a narrow topographic gap and into Bowers Basin. There is also a narrow, coherent flow eastward, and eventually southeastward, near the steep flank of Bowers Ridge. At levels ~100–300 m above the bottom, there is a suggestion of upward motion near the margins of much of the deep Bering Sea. Near-bottom geopotential gradients, referred to 3000 db, are in agreement with flow inferred from water properties

Multiple Metabolisms Constrain the Anaerobic Nitrite Budget in the Eastern Tropical South Pacific

The Eastern Tropical South Pacific is one of the three major oxygen deficient zones (ODZs) in the global ocean and is responsible for approximately one third of marine water column nitrogen loss. It is the best studied of the ODZs and, like the others, features a broad nitrite maximum across the low oxygen layer. How the microbial processes that produce and consume nitrite in anoxic waters interact to sustain this feature is unknown. Here we used 15N-tracer experiments to disentangle five of the biologically mediated processes that control the nitrite pool, including a high-resolution profile of nitrogen loss rates. Nitrate reduction to nitrite likely depended on organic matter fluxes, but the organic matter did not drive detectable rates of denitrification to N2. However, multiple lines of evidence show that denitrification is important in shaping the biogeochemistry of this ODZ. Significant rates of anaerobic nitrite oxidation at the ODZ boundaries were also measured. Lodate was a potential oxidant that could support part of this nitrite consumption pathway. We additionally observed N2 production from labeled cyanate and postulate that anammox bacteria have the ability to harness cyanate as another form of reduced nitrogen rather than relying solely on ammonification of complex organic matter. The balance of the five anaerobic rates measured—anammox, denitrification, nitrate reduction, nitrite oxidation, and dissimilatory nitrite reduction to ammonium—is sufficient to reproduce broadly the observed nitrite and nitrate profiles in a simple one-dimensional model but requires an additional source of reduced nitrogen to the deeper ODZ to avoid ammonium overconsumption. ©2017. American Geophysical Union. All Rights Reserved

Nutrient and Phytoplankton Dynamics on the Inner Shelf of the Eastern Bering Sea

In the Bering Sea, the nitrogen cycle near Nunivak Island is complicated due to limited nutrient replenishment across this broad shelf, and substantial nitrogen loss through sedimentary processes. While diffusion at the inner front may periodically support new production, the inner shelf in this region is generally described as a regenerative system. This study combines hydrographic surveys with measurements of nitrogen assimilation and benthic fluxes to examine nitrogen cycling on the inner shelf, and connectivity between the middle and inner shelves of the southern and central Bering Sea. Results establish the inner shelf as primarily a regenerative system even in spring, although new production can occur at the inner front. Results also identify key processes that influence nutrient supply to the inner shelf and reveal coupling between the middle shelf nutrient pool and production on the inner shelf

Results of the first Arctic Heat Open Science Experiment

Author Posting. © American Meteorological Society, 2018. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Bulletin of the American Meteorological Society 99 (2018): 513-520, doi:10.1175/BAMS-D-16-0323.1.Seasonally ice-covered marginal seas are among the most difficult regions in the Arctic to study. Physical constraints imposed by the variable presence of sea ice in all stages of growth and melt make the upper water column and air–sea ice interface especially challenging to observe. At the same time, the flow of solar energy through Alaska’s marginal seas is one of the most important regulators of their weather and climate, sea ice cover, and ecosystems. The deficiency of observing systems in these areas hampers forecast services in the region and is a major contributor to large uncertainties in modeling and related climate projections. The Arctic Heat Open Science Experiment strives to fill this observation gap with an array of innovative autonomous floats and other near-real-time weather and ocean sensing systems. These capabilities allow continuous monitoring of the seasonally evolving state of the Chukchi Sea, including its heat content. Data collected by this project are distributed in near–real time on project websites and on the Global Telecommunications System (GTS), with the objectives of (i) providing timely delivery of observations for use in weather and sea ice forecasts, for model, and for reanalysis applications and (ii) supporting ongoing research activities across disciplines. This research supports improved forecast services that protect and enhance the safety and economic viability of maritime and coastal community activities in Alaska. Data are free and open to all (see www.pmel.noaa.gov/arctic-heat/).This work was supported by NOAA Ocean and Atmospheric Research and the Joint Institute for the Study of the Atmosphere and Ocean (JISAO) under NOAA Cooperative Agreement NA15OAR4320063 and by the Innovative Technology for Arctic Exploration (ITAE) program at JISAO/PMEL. Jayne, Robbins, and Ekholm were supported by ONR (N00014-12-10110)

Monitoring Alaskan Arctic shelf ecosystems through collaborative observation networks

© The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Danielson, S. L., Grebmeier, J. M., Iken, K., Berchok, C., Britt, L., Dunton, K. H., Eisner, L., V. Farley, E., Fujiwara, A., Hauser, D. D. W., Itoh, M., Kikuchi, T., Kotwicki, S., Kuletz, K. J., Mordy, C. W., Nishino, S., Peralta-Ferriz, C., Pickart, R. S., Stabeno, P. S., Stafford. K. M., Whiting, A. V., & Woodgate, R. Monitoring Alaskan Arctic shelf ecosystems through collaborative observation networks. Oceanography, 35(2), (2022): 52, https://doi.org/10.5670/oceanog.2022.119.Ongoing scientific programs that monitor marine environmental and ecological systems and changes comprise an informal but collaborative, information-rich, and spatially extensive network for the Alaskan Arctic continental shelves. Such programs reflect contributions and priorities of regional, national, and international funding agencies, as well as private donors and communities. These science programs are operated by a variety of local, regional, state, and national agencies, and academic, Tribal, for-profit, and nongovernmental nonprofit entities. Efforts include research ship and autonomous vehicle surveys, year-long mooring deployments, and observations from coastal communities. Inter-program coordination allows cost-effective leveraging of field logistics and collected data into value-added information that fosters new insights unattainable by any single program operating alone. Coordination occurs at many levels, from discussions at marine mammal co-management meetings and interagency meetings to scientific symposia and data workshops. Together, the efforts represented by this collection of loosely linked long-term monitoring programs enable a biologically focused scientific foundation for understanding ecosystem responses to warming water temperatures and declining Arctic sea ice. Here, we introduce a variety of currently active monitoring efforts in the Alaskan Arctic marine realm that exemplify the above attributes.Funding sources include the following: ALTIMA: BOEM M09PG00016, M12PG00021, and M13PG00026; AMBON: NOPP-NA14NOS0120158 and NOPP-NA19NOS0120198; Bering Strait moorings: NSF-OPP-AON-PLR-1758565, NSF-OPP-PLR-1107106; BLE-LTER: NSF-OPP-1656026; CEO: NPRB-L36, ONR N000141712274 and N000142012413; DBO: NSF-AON-1917469 and NOAA-ARP CINAR-22309.07; HFR, AOOS Arctic glider, and Passive Acoustics at CEO and Bering Strait: NA16NOS0120027; WABC: NSF-OPP-1733564. JAMSTEC: partial support by ArCS Project JPMXD1300000000 and ArCS II Project JPMXD1420318865; Seabird surveys: BOEM M17PG00017, M17PG00039, and M10PG00050, and NPRB grants 637, B64, and B67. This publication was partially funded by the Cooperative Institute for Climate, Ocean, & Ecosystem Studies (CICOES) under NOAA Cooperative Agreement NA20OAR4320271, and represents contribution 2021-1163 to CICOES, EcoFOCI-1026, and 5315 to PMEL. This is NPRB publication ArcticIERP-43

The proportion of remineralized nitrate on the ice-covered eastern Bering Sea shelf evidenced from the oxygen isotope ratio of nitrate

We present measurements of nitrate and its natural abundance oxygen isotope composition (18O/16O) in the water column of the broad and shallow eastern Bering Sea shelf in the late winter and early spring of 2007 and 2008. In both years, nitrate concentrations showed a characteristic decrease, from 25 µM at the slope to ≤5 µM inshore. The 18O/16O ratio of nitrate (δ18ONO3 versus SMOW) also decreased from 3.2‰ at the slope to 1.5‰ inshore in 2007 and to as low as −1‰ inshore in 2008, indicating that nitrate inshore was nitrified at least once since having been entrained as nitrate from the slope. The shoreward decrease was less pronounced in 2007 due to 18O enrichment of nitrate from incident phytoplankton assimilation in the ice‐covered water column, whereas little to no algal growth in the water column was evident in 2008. By comparing the δ18O of nitrate to that of ambient water in spring 2008, we estimate the fraction of nitrate that was remineralized in situ rather than recently advected from the slope. These estimates indicate that 20%–100% of the nitrate in winter water of the middle and inner shelves derives from regeneration directly on the shelf rather than from the seasonal entrainment of slope waters, with recycling being the dominant mode of seasonal nitrate recharge from the 70 m isobath shoreward. These observations indicate substantial nutrient recycling on the shallow shelf, which has direct implications for the extent of fixed N loss to benthic denitrification and the fertility of the eastern shelf

Timescales of ventilation and consumption of oxygen and fixed nitrogen in the eastern tropical South Pacific oxygen deficient zone from transient tracers

The anthropogenic trace gases chlorofluorocarbon (CFC)-12 and sulfur hexafluoride (SF6) were measured during 2013 in the eastern tropical South Pacific Ocean (ETSP) offshore Chile and Peru (12°-22°S, 70°-86°W). Since the WOCE P21 line along ~17°S in 1993, the CFC-12 penetration depth increased from ~550 m to ~800 m. In 2013, CFC-12 had penetrated through the bottom of the oxygen deficient zone (ODZ, where oxygen (O2) < 4.5 μmol kg−1) at all stations, indicating that a portion of waters in this ODZ are ventilated on timescales < 60 years. Isopycnal trends in pSF6 and pCFC-12 ages versus AOU indicated oxygen utilization rates of 11.2 ± 4.7 μmol kg−1 yr−1 just above the ODZ (90–130 m) and 1.0 ± 0.5 μmol kg−1 yr−1 beneath the ODZ (400–700 m). Isopycnal trends in pSF6 ages and nutrients implied fixed N-loss rates of 0.6 ± 0.4 μmol kg−1 yr−1 at the top of the ODZ (~120 m). The pSF6 and pCFC-12 ages were significantly younger than mean ages estimated from one-dimensional transit time distributions, which were difficult to constrain using the SF6 and CFC-12 tracer combination. Despite the fact that tracer concentrations tend to underestimate mean ages, and thus overestimate nutrient regeneration/consumption rates, N-loss rates were undetectable (<0.5 μmol kg−1 yr−1) within the ODZ itself (~175–400 m). When integrated over depth, the oxygen and nitrogen consumption rates determined above and below the ODZ implied total organic carbon (C) remineralization rates on the order of 0.6 ± 0.1 mol C m−2 yr−1. These low C-export rates, and the decadal ventilation timescale of this ODZ, support a body of work suggesting that the ODZ may be sustained by inputs of high-tracer, low-oxygen waters from the adjacent Peru-Chile coastal upwelling system rather than by organic matter oxidation occurring locally

Inorganic carbon dynamics during northern California coastal upwelling

Coastal upwelling events in the California Current System can transport subsurface waters with high levels of carbon dioxide (CO 2) to the sea surface near shore. As these waters age and are advected offshore, CO 2 levels decrease dramatically, falling well below the atmospheric concentration beyond the continental shelf break. In May 2007 we observed an upwelling event off the coast of northern California. During the upwelling event subsurface respiration along the upwelling path added ∼35 μmol kg −1 of dissolved inorganic carbon (DIC) to the water as it transited toward shore causing the waters to become undersaturated with respect to Aragonite. Within the mixed layer, pCO 2 levels were reduced by the biological uptake of DIC (up to 70%), gas exchange (up to 44%), and the addition of total alkalinity through CaCO 3 dissolution in the undersaturated waters (up to 23%). The percentage contribution of each of these processes was dependent on distance from shore. At the time of measurement, a phytoplankton bloom was just beginning to develop over the continental shelf. A box model was used to project the evolution of the water chemistry as the bloom developed. The biological utilization of available nitrate resulted in a DIC decrease of ∼200 μmol kg −1, sea surface pCO 2 near ∼200 ppm, and an aragonite saturation state of ∼3. These results suggest that respiration processes along the upwelling path generally increase the acidification of the waters that are being upwelled, but once the waters reach the surface biological productivity and gas exchange reduce that acidification over time. ► Carbon transformations off US West Coast were evaluated during 3 phases of upwelling. ► Subsurface respiration on upwelling path added ∼35 μmol kg −1 of inorganic carbon. ► Respiration along upwelling path can significantly increase coastal acidification. ► Mixed layer productivity can reduce pCO 2 of the upwelled water to 200 ppm. ► Once at the surface, biology and gas exchange reduce upwelled water acidification

Estimating fixed nitrogen loss and associated isotope effects using concentration and isotope measurements of NO3–, NO2–, and N2 from the Eastern Tropical South Pacific oxygen deficient zone

Quantifying the pathways of fixed nitrogen (N) loss in marine oxygen deficient zones (ODZs) and the isotopic fractionation caused by these processes are important for understanding the marine fixed N budget and its potential for change. In this study, a variety of approaches were used to quantify fixed N loss in the eastern tropical South Pacific Ocean (ETSP). The required measurements included nutrient concentration (nitrate—NO3-, nitrite—NO2-, and phosphate—PO43-), gas ratio (N2/Ar) measurements, and stable N and O isotopes in NO3-, NO2-, and nitrogen gas (N2). The dissolved inorganic nitrogen deficit calculated from [PO43-] ([DIN]def,P) exceeded the concentration of N2 gas biologically produced in the ODZ (local [N2]bio) throughout the ODZ at most stations, likely due to release of PO43- from sediments driving up [DIN]def,P. Calculating DIN deficit using water mass analysis and local oxygen (O2) consumption ([DIN]def,OMP) yielded better agreement with local [N2]bio than [DIN]def,P, except at the maximum [N2]bio, where [DIN]def,OMP misses contributions of anaerobic ammonia oxidation (anammox) to N2 production. We used the mismatch between [DIN]def,OMP and [N2]bio to estimate a 29% contribution of anammox to [N2]bio. Stable isotopic measurements of NO2-, NO3-, and N2 were used alongside [N2]bio and new estimates of [DIN]def to calculate N and O isotope effects for NO3- reduction (15εNAR and 18εNAR, respectively), and N isotope effects for DIN removal (15εDIN-R). While the various methods for estimating [DIN]def had little effect on the isotope effects for DIN removal, differences between 15εNAR and 15εDIN-R, and variations with depth in the ODZ were observed. Using a simple time-dependent ODZ model, we interpreted these patterns to reflect the influences of NO2- oxidation and NO2- accumulation on expression of isotopic fractionation in the ODZ