Puget Sound, Washington, is both the largest fjord in the lower forty-eight states and closest to... more Puget Sound, Washington, is both the largest fjord in the lower forty-eight states and closest to the substantial urban centers of Seattle, Tacoma, Everett and surrounding communities. The sound has seasonally high annual phytoplankton standing stock and primary production, and they support several economically valuable fisheries. Our long-term goals are to develop quantitative understanding of the Sound's circulation and marine ecosystem, and of the sensitivity of the physical and the biological system to natural and human perturbations; and to develop models of Puget Sound that can aid agencies with responsibilities for environmental management in making informed decisions and serve as marine science education tools.
Slow particle remineralization, rather than suppressed disaggregation, drives efficient flux transfer through the Eastern Tropical North Pacific Oxygen Deficient Zone
Models and observations suggest that particle flux attenuation is lower across the mesopelagic zo... more Models and observations suggest that particle flux attenuation is lower across the mesopelagic zone of anoxic environments compared to oxic environments. Flux attenuation is controlled by microbial metabolism as well as aggregation and disaggregation by zooplankton, all of which shape the relative abundance of differently sized particles. Observing and modeling particle spectra can provide information about the contributions of these processes. We measured particle size spectrum profiles at one station in the oligotrophic Eastern Tropical North Pacific Oxygen Deficient Zone (ETNP ODZ) using an underwater vision profiler (UVP), a high‐resolution camera that counts and sizes particles. Measurements were taken at different times of day, over the course of a week. Comparing these data to particle flux measurements from sediment traps collected over the same time‐period allowed us to constrain the particle size to flux relationship, and to generate highly resolved depth and time estimates of particle flux rates. We found that particle flux attenuated very little throughout the anoxic water column, and at some time points appeared to increase. Comparing our observations to model predictions suggested that particles of all sizes remineralize more slowly in the ODZ than in oxic waters, and that large particles disaggregate into smaller particles, primarily between the base of the photic zone and 500 m. Acoustic measurements of multiple size classes of organisms suggested that many organisms migrated, during the day, to the region with high particle disaggregation. Our data suggest that diel‐migrating organisms both actively transport biomass and disaggregate particles in the ODZ core.
Nitrite is a key intermediate during fixed nitrogen loss in the ocean, and it accumulates within ... more Nitrite is a key intermediate during fixed nitrogen loss in the ocean, and it accumulates within marine Oxygen Deficient Zones (ODZ). ODZs are vast subsurface regions where nitrate is the dominant electron acceptor, and these regions host approximately 50% of the fixed nitrogen loss in the world's oceans. Nitrite accumulates in these waters, and recent research has discovered substantial reoxidation of nitrite back to nitrate, a significant process in the global nitrogen cycle. Partitioning between reduction and oxidation determines if marine fixed nitrogen is lost or recycled. Investigations into nitrite oxidation typically rely on results from incubations, which limits the spatiotemporal sampling coverage. Using basin‐scale data, we analyzed the ratios of nutrient regeneration within the three water masses that feed the Eastern Tropical North Pacific (ETNP) ODZ. Deviations in the ratios of nutrient regeneration from Redfield stoichiometry indicated prolific nitrite reoxidation...
The effect of interannual variation in oxygen concentration and temperature on euphausiid habitat availability in Hood Canal, WA, 2006-2015
Hood Canal has a long history of seasonal hypoxia with fish kills reported more frequently in the... more Hood Canal has a long history of seasonal hypoxia with fish kills reported more frequently in the recent decades. Because Euphausia pacifica is a dominant euphausiid species in Hood Canal and a key prey for fish, mammals, and seabirds, their responses to hypoxia and environmental changes play a key role in both ecosystem functioning and fisheries. Here, we investigate long-term variability in E. pacifica habitat availability using a combination of field observations and published data. Based on depth-stratified plankton tows at two stations in summer through fall, 2012 & 2013, we observed abundant juvenile and adult euphausiids in low dissolved oxygen waters in Hood Canal, e.g. O2/l, while their larvae showed clear avoidance of 2/l. Integrating field observations with published respiration experiments, we assess the proportion of habitats available for E. pacifica in each life stage under different temperature and oxygen they experienced in the field. Archive real-time vertical profiles of oceanographic data were obtained from the Oceanic Remote Chemical Analyzer (ORCA) buoys at multiple locations in Hood Canal. We compare temporal and spatial differences in the habitat availability during the last decade, including during “The Blob” when suitable habitats were substantially compressed for all life stages. We finally discuss the application of long-term data as a key tool to understand the challenges of future environmental change for euphausiids and, as a consequence, the food webs of temperate coastal ecosystems
Reconstructing carbonate chemistry in deep waters of the southern Salish Sea
Through survey cruises and moored time-series, we have observed the dynamic carbon cycle in vario... more Through survey cruises and moored time-series, we have observed the dynamic carbon cycle in various sub-basins of the southern Salish Sea since 2008. Areas of Puget Sound with restricted circulation, such as Hood Canal, may experience conditions of high pCO2, low pH, and low aragonite saturation state in deep waters throughout the year. Historically, the highest pCO2 and lowest pH and aragonite saturation states have been observed in early fall in Hood Canal. Upwelling of dense, nutrient- and CO2-rich but oxygen-poor water along the coast provides the marine source for Puget Sound’s deep waters. We have previously estimated that marine waters entering Puget Sound via the Strait of Juan de Fuca are now corrosive 95% of the time, representing a 26% increase in frequency since the preindustrial era. Both river inputs and intense primary production in surface waters drive remineralization of organic matter in deep waters of Puget Sound basins, contributing to the exacerbation of corrosive conditions in waters below the stratified and productive surface waters. In addition, we estimate that regionally enhanced atmospheric CO2 content may result in an increased uptake of CO2 in the region. Empirical relationships for reconstructing carbonate chemistry within Puget Sound have been created based on calibration data sets from coastal surveys, individual Puget Sound cruises, individual basins within Puget Sound, and the full Puget Sound data set (2008–2014). Here we compare their efficacy in reconstructing the evolution of carbonate system variables through seasons and across years on a profiling mooring in Hood Canal. In 2015 many features of the seasonal carbon cycle were accelerated relative to earlier years, as a result of the influence of the NE Pacific warm water anomaly. In southern Hood Canal, we saw the lowest estimated pH and aragonite saturation values in deep waters observed to date in Washington marine environments
Organic Matter and Nutrients in the Mainstem Amazon River
The Biogeochemistry of the Amazon Basin, 2001
The Amazon, like smaller rivers, is the daughter of its drainage basin. Local climate and interac... more The Amazon, like smaller rivers, is the daughter of its drainage basin. Local climate and interactions over time with the template of topography, geology, and vegetation determine the size and flow of rivers. Likewise, the compositions of the particulate and dissolved materials carried by rivers result from initially similar rainwaters that have been uniquely imprinted by contact with almost every plant, animal, and mineral in the catchment. Rivers thus provide a continuously flowing signal, recorded by isotopes, ions and molecules, of the cumulative effects of drainage basin processes such as weathering, oxidation/reduction, gas exchange, photosynthesis, biodegradation, and partitioning. This recording is complementary to more classical methods of remote sensing based on electromagnetic radiation, but is composited over a wider range of time and space scales and includes effects of subcanopy and subsurface processes. The Amazon River is similar to other rivers in this regard, but i...
Oceanic oxygen deficient zones (ODZs) influence global biogeochemical cycles in a variety of ways... more Oceanic oxygen deficient zones (ODZs) influence global biogeochemical cycles in a variety of ways, most notably by acting as a sink for fixed nitrogen (Codispoti et al. 2001). Optimum multiparameter analysis of data from two cruises in the Eastern Tropical North Pacific (ETNP) was implemented to develop a water mass analysis for the large ODZ in this region. This analysis reveals that the most pronounced oxygen deficient conditions are within the 13°C water (13CW) mass, which is distributed via subsurface mesoscale features such as eddies branching from the California Undercurrent. Nitrite accumulates within these eddies and slightly below the core of the 13CW. This water mass analysis also reveals that the 13CW and deeper Northern Equatorial Pacific Intermediate Water (NEPIW) act as the two Pacific Equatorial source waters to the California Current System. The Equatorial Subsurface Water and Subtropical Subsurface Water are synonymous with the 13CW and this study refers to this wat...
Up to half of marine N losses occur in oxygen-deficient zones (ODZs). Organic matter flux from pr... more Up to half of marine N losses occur in oxygen-deficient zones (ODZs). Organic matter flux from productive surface waters is considered a primary control on N 2 production. Here we investigate the offshore Eastern Tropical North Pacific (ETNP) where a secondary chlorophyll a maximum resides within the ODZ. Rates of primary production and carbon export from the mixed layer and productivity in the primary chlorophyll a maximum were consistent with oligotrophic waters. However, sediment trap carbon and nitrogen fluxes increased between 105 and 150 m, indicating organic matter production within the ODZ. Metagenomic and metaproteomic characterization indicated that the secondary chlorophyll a maximum was attributable to the cyanobacterium Prochlorococcus, and numerous photosynthesis and carbon fixation proteins were detected. The presence of chemoautotrophic ammonia-oxidizing archaea and the nitrite oxidizer Nitrospina and detection of nitrate oxidoreductase was consistent with cyanobacterial oxygen production within the ODZ. Cyanobacteria and cyanophage were also present on large (>30 μm) particles and in sediment trap material. Particle cyanophage-to-host ratio exceeded 50, suggesting that viruses help convert cyanobacteria into sinking organic matter. Nitrate reduction and anammox proteins were detected, congruent with previously reported N 2 production. We suggest that autochthonous organic matter production within the ODZ contributes to N 2 production in the offshore ETNP.
Anaerobic ammonium oxidation (anammox) and denitrification in Peru margin sediments
Journal of Marine Systems, 2018
Abstract The upwelling system of coastal Peru supports very high primary production, contributing... more Abstract The upwelling system of coastal Peru supports very high primary production, contributing to an oxygen deficient zone (ODZ) in subsurface waters and high organic matter deposition rates to underlying sediments. Although anammox and denitrification have been relatively well studied in ODZ waters, few studies have investigated these processes in the underlying sediments. We sampled seven stations over a large geographic area along the Peru margin, spanning a water depth of 100–3240 m. At two of the central shelf stations (100 m and 325 m), we observed Thioploca, with a well-developed mat at the shallowest station (100 m). We measured sediment properties and conducted shipboard 15N-incubations of homogenized sediments to determine potential rates of anammox and denitrification and potential controlling factors at each station. Diversity of anammox bacteria based on 16S rRNA and hydrazine oxidoreductase (hzo) sequences and hzo gene abundances were measured at each station. Overall, organic C content was high across the stations (3–12%), except for two of the deepest stations (~1.5%). Porewater ammonium fluxes and ammonium production rates in shipboard incubations, reflecting sediment organic carbon decomposition rates, were higher at the two central shelf stations compared to the other stations. The range in average potential rates was 2.1–80.4 nmol N cm−3 h−1 for denitrification and 1.8–44.2 nmol N cm−3 h−1 for anammox. The range in relative anammox (ra) across stations was 2.6–47.4%, with an average of 34.2%. The lowest ra was found at the shallowest shelf station with Thioploca mats and highest ammonium production rates. The ra jumped up to 45.9% at the station with the next highest ammonium production rates, corresponding to the deeper shelf station (325 m). At the other stations, ra was relatively high (39.6–47.4%), except at one station (16.3%), reflecting similar ammonium production rates due to decomposition across these stations. Anammox bacteria in the Candidatus Scalindua genus were the only anammox bacteria detected in Peru margin sediments based on 16S rRNA or hzo sequences. Copy number of hzo indicated abundant populations of anammox bacteria across the stations. However, hzo copy number did not correlate with anammox rates or ra. Overall, our results suggest that anammox contributes significantly to N2 production in Peru margin sediments, except in shelf sediments with high decomposition rates and dense Thioploca mats.
Nitrous oxide cycling in the Eastern Tropical South Pacific as inferred from isotopic and isotopomeric data
Deep Sea Research Part II: Topical Studies in Oceanography, 2018
Abstract The ocean accounts for up to 25% of global emissions of nitrous oxide (N2O), a potent gr... more Abstract The ocean accounts for up to 25% of global emissions of nitrous oxide (N2O), a potent greenhouse gas. Much of this N2O flux occurs in upwelling regions near the ocean's oxygen deficient zones (ODZs), areas known for intense N2O cycling. The Eastern Tropical South Pacific (ETSP) ODZ is one such area, and large uncertainties surround the balance of processes regulating N2O production and emission in this region. Here we examined the distributions of dissolved N2O concentration and stable isotopic composition, in concert with nitrate (NO3-) and nitrite (NO2-) isotopic ratios, to understand the mechanisms that drive N2O production, consumption, and emission from the ETSP ODZ. Keeling plot analysis identified N2O production from both nitrification and denitrification (or nitrifier-denitrification) in the near-surface and in the oxycline, where the largest accumulations of N2O were found. In the N2O concentration maximum that occurs below the ODZ, a higher 15N site preference (SP) indicated nitrification was more prominent. Within the ODZ, significant enrichments were apparent in δ15Nbulk (14–22‰), δ18ON2O (68–100‰) and SP (39–60‰), implying active N2O consumption. Further scrutiny of N2O isotope data in the ODZ highlights a deviation from the relative increases in δ18ON2O and SP expected for bacterial denitrification. At high levels of N2O consumption, SP increased more than expected for the increase in δ18ON2O. This appeared to be due, at least in part, to a decrease in δ15Nβ driven by N2O production in the ODZ, rather than further increases in δ15Nα. Isotopic analysis of co-occurring NO3- and NO2- suggests that NO3- may be the dominant source of N2O in the offshore ETSP ODZ.
Journal of the Fisheries Research Board of Canada, 1978
In Lake Washington, fish production through detritus-based food chains is substantially greater t... more In Lake Washington, fish production through detritus-based food chains is substantially greater than fish production through the grazing food chain. The lack of significant grazing by fish on the zooplankton is a consequence of both piscivore predation and conditions in the planktivore spawning environment. At low planktivore abundance, squawfish may switch to benthos feeding, exploiting the abundant prickly sculpin. At high planktivore abundance, squawfish feed more heavily on planktivores. Thus, even when reproductive success of planktivores is good, swamping of the squawfish population does not occur and depensatory mortality due to squawfish predation prevents planktivore abundance from increasing to the point where zooplankton resource depletion would occur. Benthic–littoral species are vulnerable to predation essentially only as larva and juveniles. They avoid predation by occupying littoral and epibenthic refugia. Recruitment to the adult population from these refugia may be ...
We review and evaluate the design and operation of twenty-seven known autonomous benthic chamber ... more We review and evaluate the design and operation of twenty-seven known autonomous benthic chamber and profiling lander instruments. We have made a detailed comparison of the different existing lander designs and discuss the relative strengths and weaknesses of each. Every aspect of a lander deployment, from preparation and launch to recovery and sample treatment is presented and compared. It is our intention that this publication will make it easier for future lander builders to choose a design suitable for their needs and to avoid unnecessary mistakes. Table . Presentation of existing landers, their constructors (with addresses), construction year(s), deployment data and the main reference(s) for each lander.
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