Trends and Relationship between Chlorophyll a and Sea Surface Temperature in the Central Equatorial Indian Ocean
Authors
Shiva Kumar, G., Satya Prakash, Ravichandran, M. And Narayana, A.C.
Source
Remote Sensing Letters, DOI 10.1080/2150704X.2016.1210835
Abstract
This work presents the trend analysis and relationship between
chlorophyll-a (chl-a) concentration and sea surface temperature
(SST) in the central equatorial Indian Ocean (CEIO) using Aqua
MODIS chl-a Level-3 Standard Mapped Image (SMI) data for a
period of 10 years (2002â¿¿2012). In order to understand the monsoonal
variability of chl-a concentration and SST and to evaluate
their relationships over the CEIO, trend analysis of chl-a values was
carried out. The area average chl-a concentration in the region
shows a weak annual cycle with high concentration during winter
(Octoberâ¿¿December) and low in summer (June). High chl-a concentration
(~0.22 mg mâ¿¿3) is observed during early winter in the
region. Chl-a concentration starts decreasing from March onwards
until the onset of summer monsoon. The data reveal low chl-a
concentrations during summer period, i.e., from June to
September, which is in accordance with several observations,
and higher concentrations during October to December. The
other reason is that satellite sensor may not capture chl-a variability
more accurately because of cloud cover during summer
monsoon time. A reasonably significant coefficient of determination
(R2 = 0.51; significant at p < 0.05 level) between SST and chl-a
concentration is recorded. This study clearly suggests that the SST
acts as a proxy for variables which cause high chl-a concentration
in the CEIO.
Paper No
2
Publication ID : 623 & Year : 2015
Title
Nitrogen uptake rates and f-ratios in the equatorial and Southern Indian Ocean
Authors
Satya Prakash, R. Ramesh, M. S. Sheshshayee, Rahul Mohan and M. Sudhakar
Source
Current Science, 108 (2). pp. 239-245
Abstract
Paper No
3
Publication ID : 622 & Year : 2015
Title
Role of cyclonic eddy in enhancing primary and new production in the Bay of Bengal
Authors
6. Singh A, Gandhi N, Ramesh R, Prakash S
Source
Journal of Sea Research, 97, 5-13
Abstract
Eddies can be important in sustaining primary production in the tropical oceans, but their role for nutrient cycling
is poorly understood in the under-sampled northern Indian Ocean. To assess the role of cyclonic eddies in
enhancing primary production, measurements of primary production were carried out at four stations in the
northern Bay of Bengal during the early winter 2007, around a cyclonic eddy close to 17.8°N, 87.5°E. Shallowing
of the thermocline and halocline by 10 m was observed within the eddy compared to the surroundings; mixed
layer depth was also reduced within the eddy. The highest surface productivity (2.71 μMCd⿿1) and chlorophyll
a (0.18 μg L⿿1)were foundwithin the eddy, and the lowest, at its outer edge. Further, the eddy supplied nutrients
to the surface layers, shallowing the subsurface chlorophyll maximum as well. Integrated production in the
euphotic top layers was more than twice within the eddy compared to its outer edge, confirming the role of
cyclonic eddies in enhancing the primary production in the otherwise less productive Bay of Bengal. Given
new nitrogen input via vertical mixing, river discharge or aerosol deposition, the additional primary production
due to this new nutrient input and its contribution to the total production (f-ratio, fraction of exportable organic
matter) increased significantly from0.4 to 0.7, and thus the Bay of Bengal can potentially transfer a high fraction
of its total production to the deep, assisted by eddies. We suggest possible improvements in experiments for
future studies, and the potential for assessing the role of eddies in biogeochemistry.
Paper No
4
Publication ID : 502 & Year : 2013
Title
Can oxycline depth be estimated using sea level anomaly (SLA) in the northern Indian Ocean?
Authors
SATYA PRAKASH, PRINCE PRAKASH and M. RAVICHANDRAN
Source
Remote Sensing Letters, Vol. 4, No. 11, 1097¿1106
Abstract
Information on depth of oxycline is critical not only for understanding magnitude and extent of the hypoxic zone but also for specifying potential fishing zones on operational basis.We analysed Argo-oxygen data from the northern Indian Ocean,
along with sea level anomaly (SLA) data from altimeter, to demonstrate the correlation
between depths of oxycline, thermocline and SLA. Our analysis suggests that observed variability in oxycline depth is mainly governed by physical processes such as vertical movement in the thermocline depth in the northern Indian Ocean
basin. There exists strong positive correlations between depths of thermocline, oxycline
and SLA. Oxycline depth and SLA are highly correlated in the Arabian Sea, but the correlation between the two is weaker in the Bay of Bengal and equatorial Indian Ocean. We propose a regression equation between SLA and oxycline depth, which may be used to estimate the depth at which water is oxygen deficient(through oxycline) in the northern Indian Ocean.
Paper No
5
Publication ID : 501 & Year : 2013
Title
Primary and new production in the thermocline ridge region of the southern Indian Ocean during the summer monsoon
Authors
Gandhi, N., Ramesh, R., Prakash, S., Noronha, S. and Anilkumar N.
Source
Journal of Marine Research, 70, 779-793
Abstract
New and primary production, measured using 15N and 13C tracers, integrated over the euphotic zone
(mostly upper 80¿100 m) varied from 7.5 to 14.1 mmol N m−2 d−1 (average 10.8 mmol N m−2 d−1)
and 2.7 to 17.7 mmol C m−2 d−1(average 11.3 mmol C m−2d−1), respectively, in the tropical India
Ocean (TIO). Shoaling of thermocline in the thermocline ridge located in the tropical Indian Ocean (TR) influences new and total productivity by supplying nutrients to the upper layers. At the same time, N-limited conditions prevail to the north of the TR region reducing biological productivity. While higher surface light intensity reduces the surface productivity, it enhances the overall depth integrated productivity. Productivity at different locations within the region is primarily controlled by the supply of N-nutrients from below. In contrast, at a given location with the available nutrient
pool, productivity at different depths is determined by light availability. The region has potential for moderate export production, as do the other parts of the Indian Ocean; the maximum possible f -ratio is found to be 0.56, suggesting that it is capable of exporting a significant part of the total production to the deep, under favorable conditions (i.e., availability of N-nutrients). A comparison with earlier data suggests no significant temporal trend in the productivity here over the past three decades.
Paper No
6
Publication ID : 415 & Year : 2012
Title
Oxycline variability in the central Arabian Sea: An Argo-Oxygen Study
Authors
Satya Prakash, T. M. Balakrishnan Nair, T V S Uday Bhaskar, Prince Prakash and Denis Gilbert
Source
Journal of Sea Research, 71, pp 1¿8
Abstract
Dissolved oxygen concentration in the oceanic waters plays a vital role in the global carbon cycle. The addition of oxygen sensors in the ongoing Argo programme could revolutionize our understanding of the ocean¿s role in climate change. Here we present a first analysis of the oxygen profiles obtained from Argo float 2900776, deployed in the oxygen minimum zone of the central Arabian Sea, one of the thickest oxygen minimum zones in the world ocean. Our study shows perennial oxygen minima in the sub-surface waters of the central Arabian Sea with strong inter-annual and intra-seasonal variability. The depth of the oxycline varies from 60 to 120 m but occasionally it may be as shallow as 40 m. It appears from the present data set that in the southeastern Arabian Sea the low oxygen water shoals up during the early winter monsoon and it is largely controlled by remote forcing. Small scale localized high wind events can cause further shoaling of the oxycline.
Paper No
7
Publication ID : 479 & Year : 2012
Title
Is the trend in chlorophyll-a in the Arabian Sea decreasing?
Authors
Prince Prakash, Satya Prakash, Hasibur Rahaman, M. Ravichandran and Shailesh Nayak
Source
Geophysical Research Letters, VOL. 39, L23605, doi:10.1029/2012GL054187
Abstract
Recent studies of satellite-derived Chlorophyll concentrations (Chl-a) in the western Arabian Sea (AS) have suggested an increasing temporal trend, but the length of the records used have typically been too short to resolve longerterm trends, if any. Our analysis of a long term satellite ocean color data shows a change of trend in the summer chlorophyll for the western AS before and after 2003; Chl-a concentration was indeed increasing till 2003, but appears to be declining since then, indicating a secular multi-year trend in Chl-a variability. However, this trend is not uniform over the entire region. Analysis of wind, sea surface temperature (SST), Sea Level Anomaly (SLA) and thermocline depth, suggests that the declining summer monsoon chlorophyll-a (Chl-a) concentration may be due to increasing SLA in this region. The earlier observed biological changes in the western AS could be an artifact of the change in local winds and ocean dynamics, which may be a part of the natural longterm
variability
Paper No
8
Publication ID : 330 & Year : 2011
Title
Nitrogen Sources for New Production in the NE Arabian Sea
Authors
Naveen Gandhi, R.Ramesh, Satya Prakash and Sanjeev Kumar
Source
Journal of Sea Research, doi:10.1016/j.seares.2010.12.002
Abstract
Paper No
9
Publication ID : 397 & Year : 2011
Title
First direct measurements of N2 fixation during a Trichodesmium bloom in the eastern Arabian Sea
Authors
Naveen Gandhi, A. Singh, Satya Prakash, R. Rengaswamy, M. Raman, M. S. Sheshshayee, and S. S. Shetye
Source
Global Biogeochem. Cycles, doi:10.1029/2010GB003970
Abstract
We report the first direct estimates of N2 fixation rates measured during the
spring, 2009 using the 15N2 gas tracer technique in the eastern Arabian Sea, which is
well known for significant loss of nitrogen due to intense denitrification. Carbon uptake
rates are also concurrently estimated using the 13C tracer technique. The N2 fixation rates
vary from ∼0.1 to 34 mmol N m−2d−1 after correcting for the isotopic under‐equilibrium
with dissolved air in the samples. These higher N2 fixation rates are consistent with
higher chlorophyll a and low d15N of natural particulate organic nitrogen. Our estimates
of N2 fixation is a useful step toward reducing the uncertainty in the nitrogen budget.
Paper No
10
Publication ID : 398 & Year : 2011
Title
Measurement of Marine Productivity using 15N and 13C tracers: Some Methodological Aspects
Authors
Naveen Gandhi, Sanjeev Kumar, Satya Prakash, R.Ramesh and M.S.Sheshshayee
Source
Journal of Earth System Science, 120(1), 99-111
Abstract
Various experiments involving the measurement of new, regenerated and total productivity using
15N and 13C tracers were carried out in the Bay of Bengal (BOB) and in the Arabian Sea. Results
from 15N tracer experiments indicate that nitrate uptake can be underestimated by experiments
with incubation time <4 hours. Indirect evidence suggests pico- and nano-phytoplankton, on their
dominance over microphytoplankton, can also influence the f-ratios. Difference in energy requirement
for assimilation of different nitrogen compounds decides the preferred nitrogen source during
the early hours of incubation. Variation in light intensity during incubation also plays a significant
role in the assimilation of nitrogen. Results from time course experiments with both 15N and 13C
tracers suggest that photoinhibition appears significant in BOB and the Arabian Sea during noon.
A significant correlation has been found in the productivity values obtained using 15N and 13C
tracers.
Paper No
11
Publication ID : 332 & Year : 2010
Title
Nitrogen uptake rates and new production in the Indian Ocean
Authors
Naveen Gandhi, Satya Prakash, R.Ramesh and Sanjeev Kumar
Source
Indian Journal of Marine Science, 39(3), 362-368
Abstract
Paper No
12
Publication ID : 331 & Year : 2010
Title
Effect of high level Iron enrichment on potential nitrogen uptake by marine plankton in the Southern Ocean
Authors
Satya Prakash, R.Ramesh, M.S.Sheshayee, Rahul Mohan and M.Sudhakar
Source
Current Science, 99(10), 1400-1404
Abstract
Paper No
13
Publication ID : 333 & Year : 2009
Title
Relative microalgal concentration in Prydz Bay, east Antarctica during late Austral Summer
