Spatial variation of phytoplankton pigments along the southwest coast of India

Phytoplankton composition and abundance were studied along the southwestern Indian coast toward the end of the upwelling season in October 2004. Phytoplankton pigment analyses, complemented by limited microscopic counts, were carried out to determine the community structure. Chlorophyll a was the most abundant of all pigments, followed by fucoxanthin. Zeaxanthin was abundantly found in the southern part of the study region (off Trivandrum), whereas fucoxanthin was the dominant marker pigment in the north (off Goa). The inferred shift in the community structure from a dominant picoplankton fraction and Prymnesiophytes to diatom-dominated microplankton toward the north is ascribed to differences in the physico-chemical environment

Applications of Machine Learning in Chemical and Biological Oceanography

Machine learning (ML) refers to computer algorithms that predict a meaningful output or categorize complex systems based on a large amount of data. ML is applied in various areas including natural science, engineering, space exploration, and even gaming development. This review focuses on the use of machine learning in the field of chemical and biological oceanography. In the prediction of global fixed nitrogen levels, partial carbon dioxide pressure, and other chemical properties, the application of ML is a promising tool. Machine learning is also utilized in the field of biological oceanography to detect planktonic forms from various images (i.e., microscopy, FlowCAM, and video recorders), spectrometers, and other signal processing techniques. Moreover, ML successfully classified the mammals using their acoustics, detecting endangered mammalian and fish species in a specific environment. Most importantly, using environmental data, the ML proved to be an effective method for predicting hypoxic conditions and harmful algal bloom events, an essential measurement in terms of environmental monitoring. Furthermore, machine learning was used to construct a number of databases for various species that will be useful to other researchers, and the creation of new algorithms will help the marine research community better comprehend the chemistry and biology of the ocean.Comment: 58 Pages, 5 Figure

Abundance and relationship of bacteria with transparent exopolymer particles during the 1996 summer monsoon in the Arabian Sea

Bacterial abundance and production, numbers, sizes and concentrations of transparent exopolymer particles (TEP) and total organic carbon (TOC) were measured during the 1996 summer monsoon to understand the relationship between TEP, the most labile particulate organic carbon, and bacteria. While high regional variability in the vertical distribution of TOC was discernible, TEP concentrations were high in surface waters at 18-20°N along 64°E with concentrations well over 25 mg alginic acid equivalents I-1 due to upwelling induced productivity. Their concentrations decreased with depth and were lower between 200 and 500 m. Bacterial concentrations were up to 1.99 × 108 I-1 in the surface waters and decreased by an order of magnitude or more at depths below 500 m. A better relationship has been found between bacterial abundance and concentrations of TEP than between bacteria and TOC, indicating that bacterial metabolism is fueled by availability of TEP in the Arabian Sea. Assuming a carbon assimilation of 33%, bacterial carbon demand (BCD) is estimated to be 1.017 to 4.035 gCm-2 d-1 in the surface waters. The observed TEP concentrations appear to be sufficient in meeting the surface and subsurface BCD in the northern Arabian Sea

Observational insights into chlorophyll distributions of subtropical South Indian Ocean eddies

publishedVersio

Remarkable structural resistance of a nanoflagellatedominated plankton community to iron fertilization during the Southern Ocean experiment LOHAFEX

The genesis of phytoplankton blooms and the fate of their biomass in iron-limited, high-nutrient−low-chlorophyll regions can be studied under natural conditions with ocean iron fertilization (OIF) experiments. The Indo-German OIF experiment LOHAFEX was carried out over 40 d in late summer 2009 within the cold core of a mesoscale eddy in the productive southwest Atlantic sector of the Southern Ocean. Silicate concentrations were very low, and phytoplankton biomass was dominated by autotrophic nanoflagellates (ANF) in the size range 3−10 μm. As in all previous OIF experiments, the phytoplankton responded to iron fertilization by increasing the maximum quantum yield (Fv/Fm) and cellular chlorophyll levels. Within 3 wk, chlorophyll levels tripled and ANF biomass doubled. With the exception of some diatoms and dinoflagellates, the biomass levels of all other groups of the phyto- and protozooplankton (heterotrophic nanoflagellates, dinoflagellates and ciliates) remained remarkably stable throughout the experiment both inside and outside the fertilized patch. We attribute the unusually high biomass attained and maintained by ANF to the absence of their grazers, the salps, and to constraints on protozooplankton grazers by heavy predation exerted by the large copepod stock. The resistance to change of the ecosystem structure over 38 d after fertilization, indicated by homogeneity at regional and temporal scales, suggests that it was locked into a stable, mature state that had evolved in the course of the seasonal cycle. The LOHAFEX bloom provides a case study of a resistant/robust dynamic equilibrium between auto- and heterotrophic ecosystem components resulting in low vertical flux both inside and outside the patch despite high biomass levels

New Species of Ciliates (Genus: <i>Strombidium </i> sp.) from hypoxic waters of the Bay of Bengal, Northern Indian Ocean

686-691Present study describes a new species of Strombidium (oligotrich ciliates) found in the cold sub-surface (125m below surface) oxic-hypoxic boundary of the Bay of Bengal. We name it as Strombidium mansai and describe its morphology

The Arabian Sea: Physical environment, zooplankton and myctophid abundance

138-145The Arabian Sea is one of the most productive regions of the world oceans. This productivity mainly results from coastal and open ocean upwelling in summer and cooling effects during winter. Earlier and more recent studies showed that there are considerable spatial and temporal variations in the area in primary productivity. Nonetheless, contrary to, earlier thinking, it would seem that the mesozooplankton abundance in the Arabian Sea is fairly high in the mixed layer all through the year. This paradox of the Arabian Sea could be partly resolved by explaining the microbial loop and a fresh set of data is presented here in support. This is because most of the herbivorous forms are either small filter feeders like copepods or larger mucous filter feeders like tunicates which are able to feed on very small particles. It would seem that the Arabian Sea sustains a large biomass of mesopelagic fishes (about 100 million tonnes), mainly myctophids. They mostly live in the core of oxygen minimum layer and ascend to the surface layers during night to feed on the abundant zooplankton

Spatial variations of DMS, DMSP and phytoplankton in the Bay of Bengal during the summer monsoon 2001

Data on the distribution of dimethylsulphide (DMS) and dimethylsulphoniopropionate (DMSP) in relation to phytoplankton abundance in different oceanic environments is important to understand the biogeochemistry of DMS, which plays an important role in the radiation balance of the earth. During the summer monsoon of 2001 measurements were made for DMS and DMSPt (total DMSP) together with related biological parameters in the Bay of Bengal. Both DMS and DMSPt were restricted to the upper 40 m of the water column. Diatoms accounted for more than 95% of the phytoplankton and were the major contributors to the DMS and DMSPt pool. The mean concentration of DMS in the upper 40 m was observed to be around 1.8 ± 1.9 nM in the study area, while DMSPt concentrations varied between 0.7 nM and 40.2 nM with a mean of 10.4 ± 8.2 nM. The observed lower DMSPt in the northern Bay in spite of higher mean primary productivity, chlorophyll a and phytoplankton cell counts seemed to result from grazing. Though salinity divides the Bay into different biogeochemical provinces there is no relation between salinity and DMS or DMSPt. On the other hand DMS was linearly related to chlorophyll a:phaeopigments ratio. The results suggest the need for deeper insight into the role of diatoms in the biogeochemical cycling of DMS

Seasonal variability in distribution and fluxes of methane in the Arabian Sea

Methane, a biogeochemically important gas in Earth/s atmosphere was measured in the water column and air in the Arabian Sea in different seasons, viz., northeast monsoon, intermonsoon, and southwest monsoon, as part of the Joint Global Ocean Flux Study (India). These observations record its distributions in the water column as well as its fluxes and their seasonal variations. Methane is mainly produced in subsurface water, and its supersaturation occurs in the upper 400 m. The CH4 peak concentration and its location vary with latitude and season. Below about 400 m, seawater CH4 concentrations, in general, are observed to be undersaturated, suggesting its consumption. Production of CH4 in oxygenated water appears to be under biological control; however, the peak in deep anoxic water does not show any particular relation with any single chemical, biological, or physical variable and rather suggests it to be maintained by the quasi-horizontal transport. The average surface supersaturations are found to be 140 &#177; 37, 173 &#177; 54, and 200 &#177; 74 in the northeast monsoon, intermonsoon, and southwest monsoon, respectively. Wind speed dependent flux estimation reveals the coastal region of the Arabian Sea to be a stronger source of methane compared to the open oceanic region, although a zonal transect along 10&#176;N also shows higher flux of methane. The effects of the findlater Jet induced downwelling on the distributions of CH4 in the near surface water as well as on its emissions have been discussed. Its annual emission rate of 0.03-0.05 Tg CH4 yr-1 from the Arabian Sea is nearly the same as that observed from the global oceans

Phytoplankton dynamics in a seasonal stratified reservoir (Tillari), Western India

Phytoplankton are the primary producers in all the aquatic ecosystems and play an important role in key biogeochemical processes that are linked to the higher trophic levels and climate variability. The present study deals with the phytoplankton dynamics, biomass and physicochemical features in freshwater reservoir, Tillari, western India. The reservoir experience seasonal stratification and mixing associated changes in the biogeochemical aspects especially the phytoplankton community and chlorophyll a (hereafter, Chl a). The influence of seasonality was lesser in the deeper water in the reservoir. Buildup in phytoplankton biomass (up to 6.6 mg m−3) was observed in the upper strata of the water column (epilimnion) during the monsoon period (June–July) and winter (December) as a result of nutrient enrichment from the hypolimnion. Among nutrients, nitrate was associated with buildup of Chl a in the epilimnion during summer (r2 = 0.7). A total of 91 phytoplankton species were identified with major contribution by charophytes and chlorophytes. The dominant phytoplankton species belonged to genera Staurastrum, Cosmarium, Aulacoseira, Nephrocytium and Shroederia. Charophytes made a remarkable presence during the whole study period in the well oxygenated epilimnion as well as in the hypolimnion with relatively low oxygen. Diatom, the major silica sinking group was relatively less abundant. Keeping the importance of the reservoir in view, the understanding of phytoplankton community from this poorly explored reservoir with respect to influencing factors is a very vital baseline information. Thus, to design and evaluate the management strategies for the reservoir, continuous monitoring and processes studies is warranted.The present study deals with the phytoplankton dynamics, biomass and physicochemical features in freshwater reservoir, Tillari, western India. The reservoir experience seasonal stratification and mixing associated and changes in the biogeochemical aspects especially the phytoplankton community and chlorophyll a. Depth affected the behavior of the phytoplankton associations. Buildup in phytoplankton biomass was observed in the upper strata of the water column (epilimnion) during the monsoon period (June-July) and winter (December) as a result of nutrient enrichment from the hypolimnion. Among nutrients, nitrate was associated with buildup of Chl a during summer in the epilimnion (r2 = 0.7). A total of about 91 phytoplankton species were identified with major contribution by charophytes and chlorophytes. The dominant phytoplankton species belonged to genera Staurastrum, Cosmarium, Aulacoseira, Nephrocytium and Shroederia. Charophytes made a remarkable presence during the whole study period in the well oxygenated epilimnion as well as in the hypolimnion with relatively low oxygen. Diatom, the major silica sinking group was relatively less abundant. Keeping the importance of the reservoir in view, the understanding phytoplankton community from this poorly explored reservoir with respect to influencing factors is a very vital baseline information. Thus, to design and evaluate the management strategies for the reservoir, continuous monitoring and processes studies is warranted