Particulate matter modulates the transport of carbon and nutrients through estuarine environments. In the Chesapeake Bay, sinking of particles and their consumption by microbes likely modulates the emergence of a seasonal oxygen deficient zone. The relationship between particle size and abundance affects transport dynamics of the particles and the biology of associated organisms. The variability of particle characteristics has not previously been characterized across the length of the Chesapeake Bay, nor has it been compared to the oxygen deficient zone. Therefore, we measured the size to mass and size to abundance relationship of suspended particles along the Chesapeake Bay during a major deoxygenation event. A laser in-situ scattering and transmissometer measured particle size and abundance at six stations. Five particle size classes were sampled at surface and bottom depths. Particles in the less saline northern end of the Bay were less massive relative to size than particles farther south. Estimates of total particle mass, calculated by combining particle size to mass and particle size to abundance data, suggested that the anoxic region has lower particulate mass than overlying oxic water, perhaps because stratified water above the oxygen minimum zone keeps particles from the productive top layer from mixing into this region. Total particle mass was higher just above the sediment, suggesting resuspension of benthic particles. Our data provide the first systematic survey of size resolved particle abundances across the Chesapeake Bay oxygen minimum zone and provide context to future work in evaluating the biogeochemical role of particles in this environment.
Marine iodine speciation has emerged as a potential tracer of primary productivity, sedimentary inputs, and ocean oxygenation. The reaction of iodide with ozone at the sea surface has also been identified as the largest deposition sink for tropospheric ozone and is also thought to be the dominant source of iodine to the atmosphere. Accurate incorporation of these processes into atmospheric models requires improved understanding of iodide concentrations at the air-sea interface. Observations of sea surface iodide are relatively sparse and are particularly lacking in the Indian Ocean basin. We present 127 new sea surface (≤10 m depth) iodide and iodate observations made during three cruises in the Indian Ocean and the Indian sector of the Southern Ocean. The observations span latitudes from ~12oN to ~70oS, and include three distinct hydrographic regimes: the South Indian subtropical gyre, the Southern Ocean and the northern Indian Ocean including the Southern Bay of Bengal. Concentrations were broadly comparable to those observed at similar latitudes in other ocean basins. The spatial distribution of sea surface iodide follows the same general trends as in other ocean basins, with iodide concentrations tending to decrease with increasing latitude (and decreasing sea surface temperature). However, the gradient of this relationship was steeper in subtropical waters of the Indian Ocean than in the Atlantic or Pacific, suggesting that it might not be accurately represented by widely used parameterisations based on sea surface temperature. Iodide concentrations in the tropical northern Indian Ocean were higher and more variable than elsewhere. Two extremely high iodide concentrations (1241 and 949 nM) were encountered in the Bay of Bengal and are thought to be associated with sedimentary inputs under low oxygen conditions. Excluding these outliers, sea surface iodide concentrations ranged from 20 to 250 nM, with a median of 61 nM. Controls on sea surface iodide concentrations in the Indian Ocean were investigated using a state-of-the-art iodine cycling model. Multiple interacting factors were found to drive the iodide distribution. Dilution via vertical mixing and mixed layer depth shoaling are key controls, and both also modulate the impact of biogeochemical iodide formation and loss processes.
A water mass analysis is a tool for interpreting the effect of ocean mixing on the distributions of trace elements and isotopes (TEI’s) along an oceanographic transect. The GEOTRACES GP15 transect along 152°W covers a wide range in latitude from Alaska to Tahiti. Our objective is to present the nutrients and hydrography of GP15 and quantify the distributions of water masses to support our understanding of TEI distributions along GP15. We used a modified Optimum Multiparameter (OMP) analysis to determine the distributions of water masses with high importance to nutrient and hydrographic features in the region. In the thermocline, our results indicated the dominance of Pacific Subarctic Upper Water (PSUW) in the subpolar gyre, Eastern North Pacific Central Water (ENPCW) in the northern subpolar gyre, and Equatorial Subsurface Water (ESSW) in the equatorial region. South Pacific Subtropical Water (SPSTW) dominated the top of the thermocline in the southern subtropical gyre, while South Pacific Central Water (SPCW) dominated the lower thermocline. Antarctic Intermediate Water (AAIW), Equatorial Intermediate Water (EqIW), and North Pacific Intermediate Water (NPIW) in the southern hemisphere, equatorial region, and northern hemisphere, respectively, occupied waters just below the thermocline. Dominant water masses in the deep waters of the southern hemisphere include Upper Circumpolar Deep Water (UCDW) and Lower Circumpolar Deep Water (LCDW) with minimal contributions from Antarctic Bottom Water (AABW). Pacific Deep Water (PDW) dominated the deep water in the northern hemisphere. Our results align well with literature descriptions of these water masses and related circulation patterns.
Atmospheric input of trace element micronutrients to the oceans is difficult to determine as even with collection of high-quality aerosol chemical concentrations such data by themselves cannot yield deposition rates. To transform these concentrations into rates, a method of determining flux by applying an appropriate deposition velocity is required. A recently developed method based on the natural radionuclide Be has provided a means to estimate the bulk (wet + dry) deposition velocity (V) required for this calculation. Here, water column Be inventories and aerosol Be concentrations collected during the 2018 US GEOTRACES Pacific Meridional Transect are presented. We use these data together with those from other ocean basins to derive a global relationship between rain rate (m/y) and bulk depositional velocity (m/d), such that V= 999±96 x Rain rate + 1040±136 (R=0.81). Thus with satellite -derived rainfall estimates, a means to calculate aerosol bulk deposition velocities is provided.
Polar marine ecosystems are particularly vulnerable to the effects of climate change. Warming temperatures, freshening seawater and disruption to sea ice formation potentially all have detrimental cascading effects on food webs. New approaches are needed to better understand spatio-temporal interactions among biogeochemical processes at the base of Southern Ocean food webs, and how these interactions vary seasonally. In marine systems, isoscapes (models of the spatial variation in the stable isotopic composition) of carbon and nitrogen identify the spatial expression of varying biogeochemical processes on nutrient utilization by phytoplankton. Isoscapes also provide a baseline for interpreting stable isotope compositions of higher trophic level animals in movement, migration and diet research. Here we produce carbon and nitrogen isoscapes across the entire Southern Ocean (>40°S) using surface particulate organic matter (POM) isotope data, collected from multiple sources over the past 50 years and throughout the annual cycle. We use Integrated Nested Laplace Approximation (INLA)-based approaches to predict mean annual isoscapes and four seasonal isoscapes using a suite of environmental data as predictor variables. Clear spatial gradients in δ13C and δ15N values were predicted across the Southern Ocean, consistent with previous statistical and mechanistic isoscape views of isotopic variability in this region. We identify strong seasonal variability in both carbon and nitrogen isoscapes, with key implications for the use of static or annual average isoscape baselines in animal studies attempting to document seasonal migratory or foraging behaviours.
Increasing CO2 in the ocean leads to warming, reduced pH (ocean acidification), and lower oxygen content in deeper ocean waters. Warming, ocean acidification, and hypoxia in deep ocean waters can have important consequences for nearshore marine ecosystems especially for regions with seasonal upwelling such as the California Current. In these regions, seasonal upwelling combined with internal waves brings low pH, low oxygen waters into nearshore reefs where animals are exposed to intermittent stressful conditions. We compared exposure between present-day and future climate scenarios (RCP85) using ROMS coupled with a biogeochemical model.
Pialassa Baiona is a shallow temperate coastal lagoon influenced by a variety of factors, including regional climate change and local anthropogenic disturbances. To better understand how these factors influenced modern organic carbon (OC) sources and accumulation, we measured OC as well as stable carbon isotopes (d13C) in 210Pb-dated sediments within a vegetated saltmarsh habitat and a human impacted habitat. Relative Sea Level (RSL) at the nearby tide gauge station data and four different Sea Surface Temperature (SST) data sets were analyzed starting from 1900 to assess the potential effect of sea ingression and warming on the coastal lagoon sedimentary process. The source contribution calculated from the MixSIAR Bayesian model revealed a mixed sedimentary organic matter (OM) composition dominated by increasing marine-derived OM after the 1950s, parallel with decreasing autochthonous saltmarsh vegetation (Juncus spp.) in the saltmarsh habitat and riverine-estuarine-derived OM in the impacted habitat. RSL rise in the area (8.7±0.5 mm yr−1 in the period 1900-2014) has been mainly driven by the land subsidence, especially during the central decades of the last century, enhancing the sea ingression in the lagoon. Annual SST anomalies present, starting from the eighties, a continuous warming tendency from 0.034±0.01 to 0.044±0.009°C yr-1. No direct effect on sedimentary properties was detected; however, RSL influenced OM sediment properties, although this effect was different between the two habitats.
Carbon and nitrogen dynamics in the Sea of Japan (SOJ) are rapidly changing. In this study, we investigated the carbon and nitrogen isotope ratios of particulate organic matter (δ13CPOM and δ15NPOM, respectively) at depths of ≤ 100 m in the southern part of the SOJ from 2016 to 2021. δ13CPOM and δ15NPOM exhibited multimodal distributions and were classified into four classes (I–IV) according to the Gaussian mixed model. A majority of the samples were classified as class II (n = 441), with mean ± standard deviation of δ13CPOM and δ15NPOM of –23.7 ± 1.2‰ and 3.1 ± 1.2‰, respectively. Compared to class II, class I had significant low δ15NPOM (-2.1 ± 0.8‰, n = 11), class III had low δ13CPOM (-27.1 ± 1.0‰, n = 21), and class IV had high δ13CPOM (-20.7 ± 0.8‰, n = 34). A majority of the class I samples were collected in winter and had comparable Japanese local rivers' origin temperature and salinity. The generalized linear model demonstrated that the temperature and chlorophyll-a concentration all had a positive effect on δ13CPOM, supporting the active photosynthesis and phytoplankton growth increased δ13CPOM. However, the fluctuation in δ15NPOM was attributed to the temperature and salinity rather than nitrate concentration. These findings suggest that multiple nitrogen sources, including nitrates from the East China Sea, Kuroshio, and Japanese local rivers, contribute to the primary production in the SOJ.
The water mass assembly of Nares Strait is variable, owing to fluctuating wind forcings over the Arctic Basins, and irregular northward flows from the West Greenland Current (WGC) in Baffin Bay. Here we characterize the physico-chemical properties of the water masses entering Nares Strait in August 2014, and we employ an extended optimum multi-parameter (OMP) water mass analysis to estimate the mixing fractions of predefined source water masses, and to distinguish the role of physical and biological processes in governing the distribution of dissolved inorganic carbon (DIC) in Nares Strait. We show the first documented evidence of Siberian shelf waters in Nares Strait, along with a diluted upper halocline layer of partial Pacific-origin. These mixed-origin water masses appear to play an important role in driving a modest phytoplankton bloom in Kane Basin, leading to decreased surface pCO2 concentrations in Nares Strait. Although inorganic nitrogen was already limited in the surface mixed layer in northern Nares Strait, the unique properties of mixed Atlantic-Pacific water facilitated upwelling and nutrient supply to the surface. These observations suggest that the positioning of the Transpolar Drift, and hence the balance of Atlantic and Pacific water delivered to Nares Strait, is likely to play an important role in regional biological productivity and carbon uptake from the atmosphere. We also observed water masses from the WGC transported as far north as Kane Basin, contributing to relatively high pCO2 and low pH in the intermediate and deep water column of southern Nares Strait and northern Baffin Bay.