Abstract. The late stage of the North East Atlantic (NEA) spring bloom was investigated during June 2005 along a transect section from 45 to 66° N between 15 and 20° W in order to characterize the contribution of siliceous and calcareous phytoplankton groups and describe their distribution in relation to environmental factors. We measured several biogeochemical parameters such as nutrients, surface trace metals, algal pigments, biogenic silica (BSi), particulate inorganic carbon (PIC) or calcium carbonate, particulate organic carbon, nitrogen and phosphorus (POC, PON and POP, respectively), as well as transparent exopolymer particles (TEP). Results were compared with other studies undertaken in this area since the JGOFS NABE program. Characteristics of the spring bloom generally agreed well with the accepted scenario for the development of the autotrophic community. The NEA seasonal diatom bloom was in the late stages when we sampled the area and diatoms were constrained to the northern part of our transect, over the Icelandic Basin (IB) and Icelandic Shelf (IS). Coccolithophores dominated the phytoplankton community, with a large distribution over the Rockall-Hatton Plateau (RHP) and IB. The Porcupine Abyssal Plain (PAP) region at the southern end of our transect was the region with the lowest biomass, as demonstrated by very low Chla concentrations and a community dominated by picophytoplankton. Early depletion of dissolved silicic acid (DSi) and increased stratification of the surface layer most likely triggered the end of the diatom bloom, leading to coccolithophore dominance. The chronic Si deficiency observed in the NEA could be linked to moderate Fe limitation, which increases the efficiency of the Si pump. TEP closely mirrored the distribution of both biogenic silica at depth and prymnesiophytes in the surface layer suggesting the sedimentation of the diatom bloom in the form of aggregates, but the relative contribution of diatoms and coccolithophores to carbon export in this area still needs to be resolved.
Improving forecasts of salinity from coastal hydrodynamic models would further our predictive capacity of physical, chemical, and biological processes in the coastal ocean. However, salinity is difficult to estimate in coastal and estuarine waters at the temporal and spatial resolution required. Retrieving sea surface salinity (SSS) using satellite ocean color radiometry may provide estimates with reasonable accuracy and resolution for coastal waters that could be assimilated into hydrodynamic models to improve SSS forecasts. We evaluated the applicability of satellite SSS retrievals from two algorithms for potential assimilation into National Oceanic and Atmospheric Administration's Chesapeake Bay Operational Forecast System (CBOFS) hydrodynamic model. Of the two satellite algorithms, a generalized additive model (GAM) outperformed that of an artificial neural network (ANN), with mean bias and root-mean-square error (RMSE) of 1.27 and 3.71 for the GAM and 3.44 and 5.01 for the ANN. However, the RMSE for the SSS predicted by CBOFS (2.47) was lower than that of both satellite algorithms. Given the better precision of the CBOFS model, assimilation of satellite ocean color SSS retrievals will not improve CBOFS forecasts of SSS in Chesapeake Bay. The bias in the GAM SSS retrievals suggests that adding a variable related to precipitation may improve its performance.
Seasonal upwelling events along the Galician coastline of the North Atlantic furnish the upper
watercolumn with nutrients, resulting in strong summer phytoplankton blooms and the sustenance of
one of Europe’s largest fisheries. The episodic nature of these upwelling events result in considerable
challenges studying the region using traditional shipboard observations. This thesis demonstrates an
alternative sampling technique, providing high spatial and temporal resolution biogeochemical data
through the use of an autonomous underwater gliderthe
Seaglider.
SG510 “Orca” was outfitted with sensors to measure dissolved oxygen, temperature,
salinity, chlorophyll a (chl a), coloured dissolved organic material (CDOM) and optical backscatter.
Deployed for 113 days over summer 2010, Orca completed 17 zonal transects across the shelf,
continental slope and open ocean at 42.1° N. Data collected during the campaign was used to
assess both the physics of the watercolumn, and the effect these physical processes have on the
region’s biogeochemistry. As part of this biogeochemical study, a novel attempt at calculating net
community production (NCP) was completed using an oxygen inventory technique.
Two major phytoplankton bloom events occurred during the deployment period, with
respective peak Chl a concentrations of 9.65 and 11.23 mg m3.
During these bloom events, NCP
varied between (net autotrophic) values of 25 and 123 (±17 ) mmol m2.
d1.
Negative values of
NCP were only observed twice for 24 and 60 hours respectively, with a maximum heterotrophy of
44
(±17) mmol m2
d1.
Overall, the summer season featured a net autotrophic metabolic balance of
+27 mmol m2
d1
.thus highlighting the importance of the region for net carbon sequestration.
Finally, this thesis also demonstrates the success of using autonomous glider platforms for sustained
biogeochemical and physical observations within a highly dynamic and challenging operational
environment with strong currents and considerable shipping traffic.
The transport of neritic carbonate sediments suspended by strong sustained winds has been observed from land and from low-altitude aircraft. In March 1996, following a sustained gale-force wind event, aerial photographs of offbank sediment transport plumes from the Bahamas Banks were obtained, and these photographs were correlated with Advanced Very High Reflectance Radiometer (AVHRR) reflectance images which showed significantly increased reflectance on the Banks due to suspended sediments. Earlier manuscripts by the authors suggested that new visible-light oceanographic remote sensing satellites, notably the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) and the Moderate Resolution Imaging Spectroradiometer (MODIS), should be capable of detecting similar sediment plumes induced by meteorological events, despite inherent difficulties of satellite remote sensing. In 1999, Hurricanes Floyd and Gert induced sediment plumes on the Bahamas Banks (Floyd) and Bermuda (Gert) that were observed by SeaWiFS. These observations validated the concept of observing neritic carbonate transport from satellites, and also provided important information about the magnitude of the meteorological events that are required to produce plumes large enough to be observed from space. Increased reflectance due to sediment suspension (i.e., turbidity) in the shallow waters overlying carbonate platforms will likely be accompanied by some amount of offbank sediment transport. Therefore, satellite observation of "increased reflectance events", which is significantly easier than observation of nearshore sediment plumes, can provide data on transport occurrence frequency. Such an observational program can contribute to improved estimates of the mass of neritic carbonate that is transported from shallow carbonate platforms. The 1999 interaction of Typhoon Dan with a shallow carbonate platform in the South China Sea (Tungsha Tao) demonstrates the feasibility of monitoring candidate environments.
Carbonates are the largest reservoirs of carbon on Earth. From mid‐Mesozoic time, the biologically catalyzed precipitation of calcium carbonates by pelagic phytoplankton has been primarily due to the production of calcite by coccolithophorids. In this paper we address the physical and chemical processes that select for coccolithophorid blooms detected in Sea‐viewing Wide Field‐of‐view Sensor (SeaWiFS) ocean color imagery. Our primary goal is to develop both diagnostic and prognostic models that represent the spatial and temporal dynamics of coccolithophorid blooms in order to improve our knowledge of the role of these organisms in mediating fluxes of carbon between the ocean, the atmosphere, and the lithosphere. On the basis of monthly composite images of classified coccolithophorid blooms and global climatological maps of physical variables and nutrient fields, we developed a probability density function that accounts for the physical chemical variables that predict the spatiotemporal distribution of coccolithophorids in the world oceans. Our analysis revealed that areas with sea surface temperatures (SST) between 3° and 15°C, a critical irradiance between 25 and 150 μmol quanta m −2 s −1 , and decreasing nitrate concentrations (ΔN/Δt < 0) are selective for upper ocean large‐scale coccolithophorid blooms. While these conditions favor both Northern and Southern Hemisphere blooms of the most abundant coccolithophorid in the modern oceans, Emiliania huxleyi , the Northern and Southern Hemisphere populations of this organism are genetically distinct. Applying amplified fragment length polymorphism as a marker of genetic diversity, we identified two major taxonomic clades of E. huxleyi ; one is associated with the Northern Hemisphere blooms, while the other is found in the Southern Hemisphere. We suggest a rule of “universal distribution and local selection”: that is, coccolithophorids can be considered cosmopolitan taxa, but their genetic plasticity provides physiological accommodation to local environmental selection pressure. Sea surface temperature, critical irradiance, and ΔN/Δt were predicted for the years 2060–2070 using the NCAR Community Climate System Model to generate future monthly probability distributions of coccolithophorids based upon the relationships observed between the environmental variables and coccolithophorid blooms in modern oceans. Our projected probability distribution analysis suggests that in the North Atlantic, the largest habitat for coccolithophorids on Earth, the areal extent of blooms will decrease by up to 50% by the middle of this century. We discuss how the magnitude of carbon fluxes may be affected by the evolutionary success of coccolithophorids in future climate scenarios.
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