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A coupled bio‐physical ocean model is used to describe areas of enhanced phytoplankton biomass, seen in remotely sensed observations, in the otherwise oligotrophic environment of the Bay of Bengal. The model is based on the Naval Coastal Ocean Model (NCOM), which is one‐way coupled to the 13‐component Carbon, Silicate, and Nitrogen Ecosystem (CoSiNE) model and configured for the Indian Ocean. Model results are compared and evaluated against a set of in situ shipboard observations as well as ocean color data acquired from several remote sensing platforms. The model is shown to successfully simulate the seasonal cycle of phytoplankton, the markedly contrasting scenarios of phytoplankton distribution in the north versus the south Bay of Bengal, and the biological impact from the 1997/1998 Indian Ocean Dipole (IOD) event. The model simulation provides us with vertical cross sections of phytoplankton biomass from summer and winter blooms in the southwest of the bay, information not found in remotely sensed data. It also successfully reproduces the timing of the onset of the blooms and their spatial extent, thereby providing a measure of its potential for augmenting in situ and remotely sensed observations to improve understanding of the dynamics of primary producers and carbon cycling in one of the most poorly sampled regions of the world's oceans. Coupled bio‐physical model configured for the Indian OceanDescription of areas of enhanced phytoplankton biomass validated by remotely sensed chlorophyll aModel provides vertical cross sections of phytoplankton not available by remote sensing

Ocean reflectance inversion models (ORMs) provide a mechanism for inverting the color of the water observed by a satellite into marine inherent optical properties (IOPs), which can then be used to study phytoplankton community structure. Most ORMs effectively separate the total signal of the collective phytoplankton community from other water column constituents; however, few have been shown to effectively identify individual contributions by multiple phytoplankton groups over a large range of environmental conditions. We evaluated the ability of an ORM to discriminate between Noctiluca miliaris and diatoms under conditions typical of the northern Arabian Sea. We: (1) synthesized profiles of IOPs that represent bio-optical conditions for the Arabian Sea; (2) generated remote-sensing reflectances from these profiles using Hydrolight; and (3) applied the ORM to the synthesized reflectances to estimate the relative concentrations of diatoms and N. miliaris. By comparing the estimates from the inversion model with those from synthesized vertical profiles, we identified those conditions under which the ORM performs both well and poorly. Even under perfectly controlled conditions, the absolute accuracy of ORM retrievals degraded when further deconstructing the derived total phytoplankton signal into subcomponents. Although the absolute magnitudes maintained biases, the ORM successfully detected whether or not Noctiluca miliaris appeared in the simulated water column. This quantitatively calls for caution when interpreting the absolute magnitudes of the retrievals, but qualitatively suggests that the ORM provides a robust mechanism for identifying the presence or absence of species.

Questions of whether diurnal changes in carbon fixation affect the global carbon budget cannot be answered using the present generation of polar orbiting ocean color sensors that can only retrieve one image daily. Here, we present novel satellite‐derived indices of chlorophyll‐based production based on the Geostationary Ocean Color Imager (GOCI), whose hourly imaging capability offer the potential for direct estimates of net phytoplankton growth over hourly to seasonal time scales. Our results reveal large variations in net chlorophyll growth in the GOCI study region, both over the day and between seasons. Hourly changes in chlorophyll concentration are highest during spring while growth rates show maxima during the winter. We show seasonal relationships between growth and photon flux. Our study suggests that Geostationary Ocean Color data can be used to constrain phytoplankton productivity on diurnal time scales and be an essential tool to better understand diurnal growth patterns over large spatial regions. The rate at which microscopic ocean plants, or phytoplankton, consume carbon dioxide represents a gap in scientific knowledge that needs to be filled in order to better model the earth system. To aid in this understanding we use a novel technique that allows us to track the growth behavior of phytoplankton in the Yellow Sea and the East Sea‐Japan Sea. This is enabled by using satellite data from the Geostationary Ocean Color Imager, which has the unprecedented ability to collect quality biological information from the ocean surface each daylight hour. We find that the results, while in agreement with local observations and other satellite studies, also contain information about how phytoplankton change over daily to annual cycles and how native communities adapt in response to the annual solar cycle. This information is useful to the ocean modeling community, that seeks to understand various ways in which phytoplankton communities affect the cycling of Earth’s carbon. The Geostationary Ocean Color Instrument tracks changes in net phytoplankton growth at hourly intervalsGains, losses, and net accumulations of chlorophyll show strong diurnal and seasonal variabilitySeasonality in net growth versus light provides evidence for seasonal evolution in phytoplankton community composition The Geostationary Ocean Color Instrument tracks changes in net phytoplankton growth at hourly intervals Gains, losses, and net accumulations of chlorophyll show strong diurnal and seasonal variability Seasonality in net growth versus light provides evidence for seasonal evolution in phytoplankton community composition

Boron proxies in the calcium carbonate shells of planktic foraminifera are sensitive to seawater acidity, but B/Ca ratios and isotopic composition (i.e., δ11B) recorded by different foraminifer species grown under identical environmental conditions differ significantly and systematically. Specifically, Globigerinoides ruberdisplays higher B/Ca and δ11B than Trilobatus sacculiferand Orbulina universa. It has been hypothesized that these differences are caused by species‐specific rates of symbiont photosynthesis and habitat depth with greater symbiont photosynthesis elevating the microenvironmental pH of G. ruberrelative to T. sacculiferand O. universa. Here we test this hypothesis by applying fast repetition rate fluorometry (FRRF), Chlorophyll aquantification, and symbiont counts in laboratory grown specimens of G. ruber(pink), T. sacculiferand O. universato study species‐specific differences in symbiont photochemical quantum efficiencies. In addition, we report B/Ca shell profiles measured by laser ablation on the same specimens previously monitored by FRRF, and δ11B data of discrete populations of all three species grown under high and low light conditions in the laboratory. While the light experiments document that symbiont photosynthesis elevates pH and/or δ11B in the calcifying microenvironment of all three foraminifer species, the FRRF, Chl. aand symbiont abundance data are relatively uniform among the three species and do not scale consistently with intrashell B/Ca, or with observed species‐specific offsets in B/Ca or δ11B. Implications of these findings for foraminiferal physiology and biomineralization processes are discussed. Symbiont photosynthesis raises pH in the microenvironment of planktic foraminiferaForaminifera species‐specific offsets in boron proxies are the same in laboratory culture and in the natural oceanic environmentSymbiont photosynthesis alone does not explain species‐specific boron proxy offsets in planktic foraminifera Symbiont photosynthesis raises pH in the microenvironment of planktic foraminifera Foraminifera species‐specific offsets in boron proxies are the same in laboratory culture and in the natural oceanic environment Symbiont photosynthesis alone does not explain species‐specific boron proxy offsets in planktic foraminifera

The partial pressure of carbon dioxide (pCO2) was surveyed across the Amazon River plume and the surrounding western tropical North Atlantic Ocean (15–0°N, 43–60°W) during three oceanic expeditions (May–June 2010, September–October 2011, and July 2012). The survey timing was chosen according to previously described temporal variability in plume behavior due to changing river discharge and winds. In situsea surface pCO2and air‐sea CO2flux exhibited robust linear relationships with sea surface salinity (SSS; 15 < SSS < 35), although the relationships differed among the surveys. Regional distributions of pCO2and CO2flux were estimated using SSS maps from high‐resolution ocean color satellite‐derived (MODIS‐Aqua) diffuse attenuation coefficient at 490 nm (Kd490) during the periods of study. Results confirmed that the plume is a net CO2sink with distinctive temporal variability: the strongest drawdown occurred during the spring flood (−2.39 ± 1.29 mmol m−2d−1in June 2010), while moderate drawdown with relatively greater spatial variability was observed during the transitional stages of declining river discharge (−0.42 ± 0.76 mmol m−2d−1in September–October 2011). The region turned into a weak source in July 2012 (0.26 ± 0.62 mmol m−2d−1) when strong CO2uptake in the mid‐plume was overwhelmed by weak CO2outgassing over a larger area in the outer plume. Outgassing near the mouth of the river was observed in July 2012. Our observations draw attention to the importance of assessing the variable impacts of biological activity, export, and air‐sea gas exchange before estimating regional CO2fluxes from salinity distributions alone. The Amazon River is the world’s largest river with a watershed covering ∼3 million square miles. Its delivery of massive amounts of freshwater, organic material, and nutrients to the salty ocean produces an extensive 30–50 feet thick layer of fresher seawater, called the “plume”, floating on the surface of the tropical Atlantic. This plume is spread by winds and currents to cover an additional ∼1 million square miles of the “river‐ocean continuum”. We studied how this plume impacts the air‐sea exchange of the greenhouse gas, carbon dioxide (CO2). We combined shipboard measurements with satellite data to estimate the full regional impact (beyond what we could observe from the ship) and examined temporal variation in this exchange. We observed rapid atmospheric CO2uptake by the plume in regions dominated by algal blooms. We also observed a large CO2release from the plume near the river mouth, likely due to microbial community respiration of riverine material. Differences in the size and salinity distribution of the plume can greatly modify the plume’s impact on CO2exchange. Our observations draw attention to understanding these variable mechanisms before using the plume extent alone to estimate future impacts on carbon uptake by this key ocean region. The Amazon River plume is a net sink for atmospheric CO2Plume size and salinity distribution affect the magnitude of the regional sinkTemporal variations in the relationship between salinity and CO2 flux occur due to changing wind speed, biological activity, and export The Amazon River plume is a net sink for atmospheric CO2 Plume size and salinity distribution affect the magnitude of the regional sink Temporal variations in the relationship between salinity and CO2 flux occur due to changing wind speed, biological activity, and export

We used the 13C tracer technique in conjunction with gas chromatography‐mass spectrometry to examine the impact of ultraviolet radiation (UVR) on the patterns of biosynthesis and composition of monosaccharides in natural assemblages of phytoplankton photoadapting to high light intensities. Exposure to UVR resulted in a decrease in the rates of phytoplankton photosynthesis and a marked reduction in the rates of production and pool sizes of neutral monosaccharides within the storage carbohydrate fraction (operationally defined as carbohydrates soluble in hot water). In contrast, the biosynthesis of neutral monosaccharides associated with cell wall or structural carbohydrates (operationally defined as the fraction of carbohydrates insoluble in hot water) showed an increase in the presence of UVR, which, although marginal, was consistent from station to station. The decline in pool sizes of monosaccharides within the storage carbohydrate fraction was largely responsible for the decline in the overall carbohydrate content of the cells. The diminution in the rates of synthesis and pool sizes of glucose within this fraction represented one of the most significant differences compared to phytoplankton shielded from UVR. In the structural carbohydrate fraction, the synthesis of several component monosaccharides was consistently higher in phytoplankton exposed to UVR.