The continental shelf in the northern Gulf of Mexico experiences expansive seasonal hypoxic conditions and eutrophication‐driven acidification in bottom waters. Rising surface ocean temperatures, ...freshwater and nutrient inputs, and atmospheric CO2 will further exacerbate these conditions. Using a high‐resolution, regional circulation‐biogeochemical model, we simulated the spatiotemporal dynamics of oxygen and inorganic carbon in the northern Gulf of Mexico under present and a projected future (2100) climate state. Results indicate a modest expansion of the hypoxic zone, but more severe hypoxia and greater exposure to prolonged hypoxic conditions. The main drivers underlying these changes are a reduction in oxygen solubility (accounting for 60–74% of the change) and increased stratification (accounting for less than 40%). pH is projected to decrease across the shelf with lowest values in hypoxic waters where aragonite saturation will approach the saturation limit. In the model simulations, acidification is primarily driven by atmospheric and offshore CO2 levels, while the enhancement in stratification only accounts for 7% or less of the total change in pH. Decreased buffering capacity and increased stratification in the future will enhance respiration‐induced acidification (i.e., a decrease in bottom water pH by respired CO2), which will amplify the climate‐induced acidification. According to the model, the magnitude of future changes varies significantly from year to year. The largest effects are simulated in years with large freshwater discharge and upwelling‐favorable winds.
Plain Language Summary
The continental shelf in the northern Gulf of Mexico experiences eutrophication‐driven seasonal low‐oxygen conditions (hypoxia) and acidification (a decrease in bottom water pH by respired CO2). Rising surface ocean temperatures, freshwater and nutrient inputs, and atmospheric CO2 will further exacerbate these conditions. We simulated the variations of oxygen and inorganic carbon in the northern Gulf of Mexico at present and under a projected future (2100) climate state. Results indicate more severe and prolonged periods of hypoxia in the future due to reduced oxygen solubility in warmer waters and increased stratification. pH is projected to decrease significantly with lowest values in low‐oxygen waters. Future acidification is primarily driven by rising atmospheric and offshore CO2 levels. A decreased buffering capacity of seawater and increased stratification will enhance respiration‐induced acidification, which will further amplify the climate‐induced acidification. The magnitude of projected changes varies significantly from year to year, with the largest effects in years with large freshwater discharge and upwelling‐favorable winds.
Key Points
Hypoxia in the future is simulated to expand and become more severe due to lower O2 solubility and enhanced density stratification
Rising atmospheric pCO2 results in a large drop in pH which will be further amplified by eutrophication
The projected response to future conditions is larger in years with high freshwater discharge and upwelling‐favorable wind
The multidecadal expansion of northern Gulf of Mexico continental shelf hypoxia is a striking example of the adverse effects of anthropogenic nutrient enrichment on coastal oceans. Increased nutrient ...inputs and widespread shelf hypoxia have resulted in numerous dissolved oxygen (DO) water quality problems in nearshore coastal waters of Louisiana. A large hydrographic dataset compiled from research programs spanning 30 years and the three-dimensional hydrodynamic-biogeochemical model CGEM (Coastal Generalized Ecosystem Model) were integrated to explore the interconnections of low DO waters across the continental shelf to nearshore coastal waters of Louisiana. Cross-shelf vertical profiles showed contiguous low DO bottom waters extending from the shelf to coastal waters nearly every year in the 30+ year time series, which were concurrent with strong cross-shelf pycnoclines. A threshold Brunt–Väisälä frequency of 40 cycles h–1 was critical to maintaining the cross-shelf subpycnocline layers and facilitating the formation of a contiguous low DO water mass. Field observations and model simulations identified periods of wind-driven bottom water upwelling lasting between several days to several weeks, resulting in both physical advection of oxygen-depleted offshore waters to the nearshore and enhanced nearshore stratification. Both the upwelling of low DO bottom waters and in situ respiration were of sufficient temporal and spatial extent to drive DO below Louisiana’s DO water quality criteria. Basin-wide nutrient management strategies aimed at reducing nutrient inputs and shelf hypoxia remain essential to improving the nearshore coastal water quality across the northern Gulf of Mexico.
Understanding the role of estuarine-carbon fluxes is essential to improve estimates of the global carbon budget. Dissolved organic matter (DOM) plays an important role in aquatic carbon cycling. The ...chromophoric fraction of DOM (CDOM) can be readily detected via in situ and remotely-sensed optical measurements. DOM properties, including CDOM absorption coefficient at 412nm (ag412) and dissolved organic carbon (DOC) concentrations were examined in Apalachicola Bay, a national estuarine research reserve located in the northeast Gulf of Mexico, using in situ and satellite observations during the spring and fall of 2015. Synoptic and accurate representation of estuarine-scale processes using satellite ocean color imagery necessitates the removal of atmospheric contribution (~90%) to signals received by satellite sensors to successfully link to in situ observations. Three atmospheric correction schemes (e.g., Standard NIR correction, Iterative NIR correction, and SWIR correction) were tested first to find a suitable correction scheme for the VIIRS imagery in low to moderately turbid Apalachicola Bay. The iterative NIR correction performed well, and validation showed high correlation (R2=0.95, N=25) against in situ light measurements. A VIIRS-based CDOM algorithm was developed (R2=0.87, N=9) and validated (R2=0.76, N=20, RMSE=0.29m−1) against in situ observations. Subsequently, ag412 was used as a proxy of DOC in March (DOC=1.08+0.94×ag412, R2=0.88, N=13) and in November (DOC=1.61+1.33×ag412, R2=0.83, N=24) to derive DOC maps that provided synoptic views of DOC distribution, sources, and their transport to the coastal waters during the wet and dry seasons. The estimated DOC stocks were ~3.71×106kg C in March and ~4.07×106kg C in November over an area of ~560km2. Volume flux (out of the bay) almost doubled for March 24 (735m3s−1) relative to November 4 (378m3s−1). However, estimates of DOC fluxes exported out of the bay from model-derived currents and satellite-derived DOC were only marginally greater in March (0.163×106kgCd−1) than in November (0.124×106kgCd−1) and reflected greater DOC stocks in the fall. The combination of satellite-, field-, and model-based observations revealed the strong linkage between the Apalachicola River plume, a major source of DOM, and the overall hydrodynamic forcing that controlled distributions of CDOM abundance, DOC concentration, stocks, and fluxes in the bay.
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•A VIIRS-based CDOM empirical algorithm is presented for Apalachicola Bay.•Distributions of ag412 and DOC were examined in conjunction with forcing factors.•DOM distribution, stocks and fluxes examined using field, satellite and model data.•DOC standing stocks were greater in fall but fluxes marginally greater in spring.
An array of three bottom-mounted ADCP moorings was deployed on the prevailing propagation path of strong internal tides for nearly 1 year across the continental slope in the northern South China Sea. ...These velocity measurements are used to study the intra-annual variability of diurnal and semidiurnal internal tidal energy in the region. A numerical model, the Luzon Strait Ocean Nowcast/Forecast System developed at the U.S. Naval Research Laboratory that covers the northern South China Sea and the Kuroshio, is used to interpret the observed variation of internal tidal energy on the Dongsha slope. Internal tides are generated primarily at the two submarine ridges in the Luzon Strait. At the western ridge generation site, the westward energy flux of the diurnal internal tide is sensitive to the stratification and isopycnal slope associated with the Kuroshio. The horizontal shear at the Kuroshio front does not modify the propagation path of either diurnal or semidiurnal tides because the relative vorticity of the Kuroshio in Luzon Strait is not strong enough to increase the effective inertial frequency to the intrinsic frequency of the internal tides. The variation of internal tidal energy on the continental slope and Dongsha plateau can be attributed to the variation in tidal beam propagation in the northern South China Sea.
In the western North Pacific subtropical ocean, the Anatahan volcano of the Mariana Islands erupted on 10 May 2003 for the first time in recorded history. Based on nine different types of remote ...sensing data provided by NASA, laboratory experiment of the Anatahan samples, and a 3‐D ocean circulation model developed by the U.S. Naval Research Laboratory, the postvolcanic ocean biogeochemical response to the Anatahan eruption was explored. It was observed that soon after the eruption, the aerosol optical depth abruptly increased from the pre‐eruption loading of ∼0.1 to ∼2. In the week following the eruption, a “bloom‐like” patch was observed by NASA's Aqua Moderate Resolution Imaging Spectroradiometer (MODIS) ocean color sensor. Based on the chlorophyll a, fluorescence line height (FLH), at‐sensor total radiance, and normalized water‐leaving radiance data obtained by MODIS, the cause of the bloom‐like patch was diagnosed. The results suggest that the patch was most likely a mixture of suspended volcanic particles and a phytoplankton bloom. FLH was found to be ∼9–17 × 10−3 mW cm−2μm−1 sr−1 in the patch and ∼3–5 × 10−3 mW cm−2μm−1 sr−1 in the ambient water, indicating that a 2–5‐fold increase in biological activity occurred during the week following the eruption. Satellite altimetry indicated that the bloom took place in the presence of downwelling and was not a result of upwelled nutrients in this oligotrophic ocean. Analysis of satellite ocean color spectra of the bloom region found similar spectra as the reference Trichodesmium spectra. Laboratory experiments further substantiate the satellite observations which show elevated concentrations of limiting nutrients provided by the Anatahan samples, and the averaged soluble nitrate, phosphate, and Fe were 42, 3.1, and 2.0 nM, respectively. Though it was not possible to obtain in situ observations of the ocean biogeochemical responses that followed the Anatahan eruption, this study provided evidence based on remote sensing data and laboratory experiment that fertilization of volcanic aerosols occurred following this eruption in one of the most oligotrophic low‐nutrient low‐chlorophyll ocean deserts on Earth.
Abstract
Photosynthetically available radiation (PAR) incident at the sea surface penetrates into the water column and drives oceanic primary production. Ecosystem models to estimate phytoplankton ...biomass and primary production require an estimate of sea surface PAR, which is available from satellite ocean color imagery and atmospheric model predictions. Because the PAR values could come from either source, it is important to understand the variability and accuracies of each. We performed spatial and temporal analyses covering multiple years and seasons, and clear/cloudy conditions. We compare values derived from the imagery to those from the models and to in situ measurements in the Gulf of Mexico to validate the imagery and models and to assess PAR variability based on source. Averaged over space or time, the relative errors in PAR between the six sources (two satellite, three model, and in situ) are generally less than 5%–7%, but they can vary up to 11%. However, the errors and biases on a daily or pixel-by-pixel basis are larger, and the averages can mask seasonal trends.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Internal solitary waves are ubiquitous in coastal regions and marginal seas of the world’s oceans. As the waves shoal shoreward, they lose the energy obtained from ocean tides through globally ...significant turbulent mixing and dissipation and consequently pump nutrient-rich water to nourish coastal ecosystem. Here we present fine-scale, direct measurements of shoaling internal solitary waves in the South China Sea, which allow for an examination of the physical processes triggering the intensive turbulent mixing in their interior. These are convective breaking in the wave core and the collapse of Kelvin–Helmholtz billows in the wave rear and lower periphery of the core, often occurring simultaneously. The former takes place when the particle velocity exceeds the wave’s propagating velocity. The latter is caused by the instability induced by the strong velocity shear overcoming the stratification. The instabilities generate turbulence levels four orders of magnitude larger than that in the open ocean.
Fine-scale, direct measurements of shoaling internal solitary waves reveal that convective breaking and collapse of Kelvin–Helmholtz billows often occur simultaneously and generate turbulence four orders of magnitude larger than in the open ocean.
The formation of arc-type structures in the surface elevation and temperature fields due to internal tidal (IT) waves is studied in the region of the South China Sea (SCS) and Luzon Strait. It is ...demonstrated that these arc-type structures in the surface elevation and temperature at depth result from the merging of IT waves. Predictions of internal baroclinic tides are conducted with a nonlinear hydrostatic model, the Luzon Strait Nowcast/Forecast System, forced with tides, realistic surface forcing and stratification (
Appendix 1
). It is shown that IT waves generated by the undersea ridges near the Batan and Babuyan Islands in the Luzon Strait propagate westward and merge into arcs in the SCS. The superposition of IT waves is also investigated with a linear knife-edge model (
Appendix 2
). M
2
and K
1
tidal waves are considered. It is demonstrated that K
1
, M
2
tidal waves from the Babuyan Islands combine with waves from the Batan Islands to form arc signatures in sea surface elevation and warm spots in the South China Sea. Possible modulation effects of K
1
waves on M
2
waves are shown. Dynamics of the nonlinear hydrostatic model shape the arc segments differently from the linear model. Arc lengths increase from the sources in nonlinear and linear models. The model-predicted merged IT waves are compared with SAR images.
Hurricanes are increasingly being recognized as important episodic drivers in ocean biogeochemical cycling; however, spatiotemporal response of their impacts on coastal and estuarine ecosystems are ...limited. Hurricane Michael, which made landfall just west of Apalachicola Bay (ApB) on October 10, 2018 as a Category 5 hurricane with sustained winds of 250 km h-1, caused widespread damage to the northwest Florida coast, and adverse effects on oyster reefs and water quality in ApB due to winds and coastal flooding associated with a strong storm surge. The impact of wind forcing and retreating storm surges on coastal and shelf biogeochemical properties remains however, largely unknown. In this study, we use a combination of pre-hurricane field observations, ocean-color satellite imagery and the outputs (salinity, currents, sea surface height and temperature) of a nested high-resolution 3-dimensional hydrodynamic model (NCOM) to examine the biogeochemical response of ApB and the surrounding shelf waters to Hurricane Michael. MODIS-derived optical proxies (e.g., absorption of colored dissolved organic matter or CDOM and particle backscattering coefficients) of dissolved and particulate organic carbon (DOC and POC) were derived for a series of clear-sky imagery (prior to and following the hurricane) using a combination of estuarine-tuned semi-analytic and empirical algorithms. Following the hurricane, spatiotemporal distribution of both DOC and POC in ApB and the nearshore coastal waters showed a strong response to storm surge, increasing river discharge, currents, and wind field. Average flux estimates of organic carbon exported from ApB between October 5-21, 2018 to the coastal ocean were much greater for DOC (0.86106 kg C d-1) than POC (0.21106 kg C d-1) and increased with increasing river discharge and the wind field. A bio-optical inversion algorithm applied to Sentinel-3A OLCI imagery of 13 October, 2018 immediately following the hurricane’s passage, showed a strong, week-long biological response with spatially distinct phytoplankton blooms of Karenia brevis and Emiliania Huxleyi, as detected by satellite imagery of pigments, an approach that could revolutionize our understanding of environmental impacts on phytoplankton. This study revealed spatiotemporal changes in estuarine and coastal ocean biogeochemistry reflective of a systematic regional ecosystem response to Hurricane Michael.
Background
A phase I clinical study for patients with locally advanced H&N cancer with a new class of botanical drug APG‐157 provided hints of potential synergy with immunotherapy. We sought to ...evaluate the efficacy of the combination of APG‐157 and immune checkpoint inhibitors.
Methods
CCL23, UM‐SCC1 (human), and SCCVII (HPV−), MEER (HPV+) (murine) H&N cancer cell lines were utilized for in vitro and in vivo studies. We measured tumor growth by treating the mice with APG‐157, anti‐PD‐1, and anti‐CTLA‐4 antibody combinations (8 groups). The tumor microenvironments were assessed by multi‐color flow cytometry, immunohistochemistry, and RNA‐seq analysis. Fecal microbiome was analyzed by 16S rRNA sequence.
Results
Among the eight treatment groups, APG‐157 + anti‐CTLA‐4 demonstrated the best tumor growth suppression (p = 0.0065 compared to the control), followed by anti‐PD‐1 + anti‐CTLA‐4 treatment group (p = 0.48 compared to the control). Immunophenotype showed over 30% of CD8+ T cells in APG‐157 + anti‐CTLA‐4 group compared to 4%–5% of CD8+ T cells for the control group. Differential gene expression analysis revealed that APG‐157 + anti‐CTLA‐4 group showed an enriched set of genes for inflammatory response and apoptotic signaling pathways. The fecal microbiome analysis showed a substantial difference of lactobacillus genus among groups, highest for APG‐157 + anti‐CTLA‐4 treatment group. We were unable to perform correlative studies for MEER model as there was tumor growth suppression with all treatment conditions, except for the untreated control group.
Conclusions
The results indicate that APG‐157 and immune checkpoint inhibitor combination treatment could potentially lead to improved tumor control.
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