Dr-Avinash Kumar | National Centre For ANTARCTIC AND OCEAN RESEARCH (original) (raw)

Papers by Dr-Avinash Kumar

Deep Sea Research Part I: Oceanographic Research Papers, 2013

Expansio have sev global pr viewing 2010) su average a accompa ± 0.0001 temperatu factors c ation... more Expansio have sev global pr viewing 2010) su average a accompa ± 0.0001 temperatu factors c ation of olig and biologic is much higher than the global estimates (0.18±0.05 cm/yr) reported in the Intergovernmental Panel on Climate Change report, 2007. The variability in Chl-a concentration was also studied with respect to leading climate oscillators.

Geoscience Frontiers, 2015

ABSTRACT The spatial distribution patterns of surficial sediment samples from different sedimenta... more ABSTRACT The spatial distribution patterns of surficial sediment samples from different sedimentary domains (shallow to deep-sea regions) of the eastern Arabian Sea were studied using sediment proxies viz. environmental magnetism, geochemistry, particle size and clay mineralogy. Higher concentrations of magnetic minerals (high χlf) were recorded in the deep-water sediments when compared with the shallow water sediments. The magnetic mineralogy of one of the shallow water samples is influenced by the presence of bacterial magnetite as evidenced from the χARM/χlfvs. χARM/χfd biplot. However, the other samples are catchment-derived. The high correlation documented for χlf, anhysteretic remanent magnetisation (χARM) and isothermal remanent magnetisation (IRM) with Al indicates that the deep-sea surficial sediments are influenced by terrigenous fluxes which have been probably derived from the southern Indian rivers, the Sindhu (the Indus) and the Narmada-Tapti Rivers. A lower Mn concentration is recorded in the upper slope sediments from the oxygen minimum zone (OMZ) but a higher Mn/Al ratio is documented in the lower slope and deep-sea sediments. Clay minerals such as illite (24–48.5%), chlorite (14.1–34.9%), smectite (10.6–28.7%) and kaolinite (11.9–27.5%) dominate the sediments of shallow and deep-sea regions and may have been derived from different sources and transported by fluvial and aeolian agents. Organic carbon (OC) data indicate a low concentration in the shallow/shelf region (well oxygenated water conditions) and deeper basins (increased bottom-water oxygen concentration and low sedimentation rate). High OC concentrations were documented in the OMZ (very low bottom-water oxygen concentration with high sedimentation rate). The calcium carbonate concentration of the surface sediments from the continental shelf and slope regions (<1800 m) up to the Chagos-Laccadive Ridge show higher concentrations (average=58%) when compared to deep basin sediments (average=44%). Our study demonstrates that particle size as well as magnetic grain size, magnetic minerals and elemental variations are good indicators to distinguish terrigenous from biogenic sediments and to identify sediment provenance.

Heliyon , 2020

The present study quantifies the magnitude of Arctic sea-ice loss in the boreal summer (July-Sept... more The present study quantifies the magnitude of Arctic sea-ice loss in the boreal summer (July-September), especially in September at different timescales (daily, monthly, annual and decadal). The investigation on the accelerated decline in the Arctic sea-ice was performed using different datasets of passive microwave satellite imagery and model reanalysis. Arctic sea-ice declined rapidly in the boreal summer (-10.2 AE 0.8 %decade À1) during 1979-2018, while, the highest decline in sea-ice extent (SIE) (i.e., 82,300 km 2 yr À1 /-12.8 AE 1.1 %deca-de À1) is reported in the month of September. Since late 1979, the SIE recorded the sixth-lowest decline during September 2018 (4.71 million km 2). Incidentally, the records of twelve lowest extents in the satellite era occurred in the last twelve years. The loss of SIE and sea-ice concentration (SIC) are attributed to the impacts of land-ocean warming and the northward heat advection into the Arctic Ocean. This has resulted in considerable thinning of sea-ice thickness (SIT) and reduction in the multiyear ice (MYI) for summer 2018. Global and Arctic land-ocean temperatures have increased by~0.78 C and~3.1 C, respectively, over the past 40 years (1979-2018) while substantial warming rates have been identified in the Arctic Ocean (~3.5 C in the last 40-year) relative to the Arctic land (~2.8 C in the last 40-year). The prevailing ocean-atmospheric warming in the Arctic, the SIE, SIC and SIT have reduced, resulting in the decline of the sea-ice volume (SIV) at the rate of-3.0 AE 0.2 (1000 km 3 decade À1). Further, it observed that the SIV in September 2018 was three times lower than September 1979. The present study demonstrates the linkages of sea-ice dynamics to ice drifting and accelerated melting due to persistent low pressure, high air-ocean temperatures, supplemented by the coupled ocean-atmospheric forcing.

Research Article, May 29, 2015

The spatial distribution patterns of surficial sediment samples from different sedimentary domain... more The spatial distribution patterns of surficial sediment samples from different sedimentary domains (shallow to deep-sea regions) of the eastern Arabian Sea were studied using sediment proxies viz. environmental magnetism, geochemistry, particle size and clay mineralogy. Higher concentrations of magnetic minerals (high χlf) were recorded in the deep-water sediments when compared with the shallow water sediments. The magnetic mineralogy of one of the shallow water samples is influenced by the presence of bacterial magnetite as evidenced from the χARM/χlfvs. χARM/χfd biplot. However, the other samples are catchment-derived. The high correlation documented for χlf, anhysteretic remanent magnetisation (χARM) and isothermal remanent magnetisation (IRM) with Al indicates that the deep-sea surficial sediments are influenced by terrigenous fluxes which have been probably derived from the southern Indian rivers, the Sindhu (the Indus) and the Narmada-Tapti rivers. A lower Mn concentration is recorded in the upper slope sediments from the oxygen minimum zone (OMZ) but a higher Mn/Al ratio is documented in the lower slope and deep-sea sediments. Clay minerals such as illite (24–48.5%), chlorite (14.1–34.9%), smectite (10.6–28.7%) and kaolinite (11.9–27.5%) dominate the sediments of shallow and deep-sea regions and may have been derived from different sources and transported by fluvial and aeolian agents. Organic carbon (OC) data indicate a low concentration in the shallow/shelf region (well oxygenated water conditions) and deeper basins (increased bottom-water oxygen concentration and low sedimentation rate). High OC concentrations were documented in the OMZ (very low bottom-water oxygen concentration with high sedimentation rate). The calcium carbonate concentration of the surface sediments from the continental shelf and slope regions (<1800 m) up to the Chagos-Laccadive Ridge show higher concentrations (average = 58%) when compared to deep basin sediments (average = 44%). Our study demonstrates that particle size as well as magnetic grain size, magnetic minerals and elemental variations are good indicators to distinguish terrigenous from biogenic sediments and to identify sediment provenance.

Research Article, Jan 21, 2014

Changes in estuarine morphology and landforms (braided islands, mudflats, barrier spits and marsh... more Changes in estuarine morphology and landforms (braided islands, mudflats, barrier spits and marshy land) of Gangolli estuary, west coast of India, have been studied using topographic maps and satellite images of the last 45 years (1967–2012). The seasonal fluctuations in hydro-meteorological (river discharge, runoff, rainfall, relative humidity and temperature) conditions play an important role in morphological changes of landforms. The computed results were recorded no significant relationship (p > 0.050) between areal extents of the different landforms (except Is7 and Mf3) and hydro-meteorological parameters. The correlation analysis suggests that ∼65 % of the landforms show medium (r = 0.3–0.5) to high (r = 0.5–1.0) strength of association between areal extent versus discharge, runoff and temperature. However, ∼80 % of the landforms show high to medium strength of association between areal extent versus rainfall and relative humidity. The study confides that gradual accumulation of sediment brought by rivers and eventually drifted into the estuary by waves and tidal currents is responsible for stabilisation and growth of the different landforms such as estuarine banks, braided islands and spits. By contrast, both natural and anthropogenic activities have played a major role in dynamic changes of estuarine morphology and landforms of Gangolli estuary, but human interventions especially construction of harbour, sand mining and reclamation are the most significant factors.

Expansion of oligotrophic ocean gyre and widespread reduction of phytoplankton biomass will have ... more Expansion of oligotrophic ocean gyre and widespread reduction of phytoplankton biomass will have severe environmental and ecological effect since phytoplankton accounts for half of the global primary production, which forms the trophic base for marine ecosystem. Analysis of Sea-viewing Wide Field-of-view Sensor (SeaWiFS) derived chlorophyll-a (Chl-a) datasets (1998–2010) suggested significant expansion of South Indian Ocean oligotrophic gyre (SOG) at average annual rate of 4.46%/yr (r=0.66, p=0.013). The annual trend of SOG expansion was accompanied with the significantly declining trend of Chl-a concentration (−1.36%/yr, or −0.0007±0.0001 mg m−3/yr, r=0.76, p=0.002). Environmental parameters such as sea surface temperature (SST) and meridional wind stress (τyτy) were found to be the most accountable factors controlling the variability of Chl-a/gyre area. Nevertheless, SST was the dominant predictor of biological response (explains more than 60% of Chl-a variability). This study suggests that the observed trend of SOG expansion and accompanied decline in Chl-a concentration is principally due to SST warming (0.05±0.01 °C/yr, r=0.83, p=0.0008) and weakening of wind stress (ττ) mainly meridional wind stress component, τyτy (−0012 Pa/yr, r=0.86, p=0.004). Additionally, the SST trend map showed more than 80% of the SOG area is warming significantly under circumstance of overall gain of net heat flux by the sea surface. Analysis of these climate variables suggests decreased mixing and enhanced stratification in the SOG which reduces nutrient supply to sunlit zone; consequently resulting in low phytoplankton biomass, and gyre expansion. In addition, the sea-level rise observed in SOG (0.48±0.05 cm/yr) is much higher than the global estimates (0.18±0.05 cm/yr) reported in the Intergovernmental Panel on Climate Change report, 2007. The variability in Chl-a concentration was also studied with respect to leading climate oscillators.

The dynamics and factors responsible for morphological changes of spits viz., Uliyargoli-Padukere... more The dynamics and factors responsible for morphological changes of spits viz., Uliyargoli-Padukere, Oddu Bengre and Kodi Bengre, southern Karnataka, India, are investigated using multi-dated satellite images and topographic maps during the last 95-years (1910-2005). Variations and overall rate of changes in length, area and coefficient of determination (R2) of each spit are calculated separately for two periods (1910 and 1967 as base years) to find out whether there is any significant trend in the case of change in length and area in all the three spits that are under study. Linear trend lines are fitted using a least squares method and the statistical significance is considered at 80% level of confidence. The results recorded significant changes in spit morphology, especially in length and area if 1910 and 1967 are considered separately as base years, are may be due to non-availability of data set between 1910 and 1967 period. The study reveals that coastal processes, such as SW-monsoon influenced strong currents and longshore drifts are the main process for formation and growth of spits, whereas rivers influence/drift also plays significant role. The statistical uncertainty estimation in spits morphology is prevalent wherever the coast is affected by human interventions. The study demonstrates that combined use of satellite imagery and statistical techniques can be effectively used to understand the evolution of spits morphology.

""The present study indicates that coastal geomorphology is controlled by the natural processes a... more ""The present study indicates that coastal geomorphology is controlled by the natural processes and anthropogenic activities. The changes in shoreline position of Udupi coast, western India, are investigated for a period of 98 years using multi-dated satellite images and topographic maps. The study area has been divided into four littoral cells and each cell into a number of transects at uniform intervals. Further, past shoreline positions have been demarcated and future positions are estimated for 12 and 22 years. The shoreline change rate has been estimated using statistical methods—end point rate, average of rates and linear regression—and cross-validated with correlation coefficient and root-mean-square error (RMSE) methods. Resultant changes from natural processes and human interventions have been inferred from the estimated values of the back-calculated errors. About 53 % of transects exhibit ±10 m RMSE values, indicating better agreement between the estimated and satellite-based shoreline positions, and the transects closer to the cell boundaries exhibit *57 % uncertainties in shoreline change rate estimations. Based on the values of correlation coefficient and RMSE, the influence of natural processes and human interventions on shoreline changes have been calculated. The cells/ transects dominated by natural processes record low RMSE values, whereas those influenced by human interventions show lower correlation coefficient and higher RMSE values. The present study manifests that the results of this study can be very useful in quantifying shoreline changes and in prediction of shoreline positions."

""The changes in shoreline positions and morphology of spits along the Karnataka coast, western I... more ""The changes in shoreline positions and morphology of spits along the Karnataka coast, western India, are investigated for the period from 1910 to 2005 using multi-dated satellite images and topomaps. The study area has been divided into four littoral cells, and each cell into a number of transects at uniform intervals. The rate of change in shoreline position has been estimated using the statistical linear regression method and cross-validated with regression coefficient (R2) and Root Mean Square Error (RMSE) methods. Past and future shoreline positions have been demarcated and future positions of shoreline are estimated for time periods of 10- and 24-years.

The study reveals that (i) about 57% of transects exhibit ± 10 m RMSE values, indicating better agreement between the estimated and satellite-based shoreline positions, and (ii) transects closer to the cell boundaries exhibit about 50% uncertainties in shoreline change rate estimations. Based on RMSE values, the influence of natural processes and anthropogenic factors on shoreline changes has been evaluated. The cells/transects dominated by natural processes reveal low RMSE values, whereas the cells/transects influenced by anthropogenic activities such as sand mining, construction of coastal structures, exhibit higher RMSE values. However, the variation in RMSE values is not significant if the total number of transects is considered.

Significant changes in morphology of spits have been recorded. Spits demonstrate variations in areal extent, i.e., length and area, if 1910 and 1967 are considered separately as base years. The present study demonstrates that combined use of satellite imagery and statistical techniques such as linear regression and RMSEs can be very useful in quantifying shoreline changes and spit morphology.""

Eighteen kilometers long coastal stretch from the New Mangalore Port in the north toTalapadi in t... more Eighteen kilometers long coastal stretch from the New Mangalore Port in the north toTalapadi in the south has been studied in order to understand shoreline changes and erosion/ accretion patterns that have taken place due to the natural processes and anthropogenic activities. Shoreline changes and quantification of beach erosion/accretion were made using the Survey of India topomap, multidated satellite images and beach profile surveys. During 1967-97 period, most of the beaches were accreted, except those lie just towards south of the Netravati and Gurpur river mouth in Sector III. During 1997-2001 period also, the beaches showed accretion trend, but they were subjected to severe erosion during 2001-05 in all the four sectors. The beaches in Sectors I-III are polluted due to discharges of effluents and very poor maintenance.

http://link.springer.com/article/10.1007%2Fs12665-011-1128-3, Feb 2012

Qualitative and quantitative evolution of the Swarna estuary, during the past 38 years (1967–2005... more Qualitative and quantitative evolution of the Swarna estuary, during the past 38 years (1967–2005), has been analysed by integrating the results of field surveys, satellite images, hydrodynamic modelling and topographic data in GIS context. Significant changes in erosion/accretion patterns of the estuarine banks, inlet configuration and adjacent spits, and origin, morphology, orientation and areal extent of fifteen braided islands have been estimated. Hydrodynamics of the region is studied through modelling, and probable flow pattern that is responsible for morphological changes is discussed. The simulated flow patterns indicate that current speeds are of the order of 10–20 cm/s inside the estuary and of the order of 40 cm/s at the mouth. The Right bank (Rb) of the estuary is subject to net erosion and the Left bank (Lb) is subject to net accretion. On an average, 20–30% of the area of all braided islands would be flooded, if the water level rises by 0.7 to 1.0 m. Islands of this estuary are morphologically very dynamic (migrating towards north, northeast and southwest directions) and subject to net accretion, whereas only one island (i.e., the Padu) has lost its major portion of landmass. A conceptual inverse distance weighted (IDW) interpolation model has been generated and evaluated possible flooding on the estuarine shoals and braided islands, due to heavy rainfall and/or sea-level rise. The model reveals that the possibility of flooding will be higher for those islands which are located close to the Rb than those close to the Lb.

Springer, 2013

The study demonstrates the potential of geographical information system and statistical-based app... more The study demonstrates the potential of geographical information system and statistical-based approaches to identify the hydrological processes and demarcate the groundwater prospect zones of the Gangolli basin, Karnataka State, India. The basin is situated in humid tropical climate and influenced by three major rivers viz. Kollur (6th order stream), Chakra (6th order stream) and Haladi (7th order stream) which cover an area of ~1,512 km2 and cumulative length of ~84 km. Various thematic maps—drainage, geomorphology, geology, slope, soil, lineament and lineament density—were prepared using Survey of India topographic maps, Indian remote sensing (IRS-P6) images and other published maps. Hydrogeomorphologic characteristics were correlated with different morphometric parameters to identify the hydrological processes and demarcate the groundwater potential zones of the basin. All the hydrological units and morphometric parameters were assigned suitable weightages according to their relative importance to groundwater potentiality to identify the most deficit/surplus zones of groundwater. Based on hydrological characteristics, integrated thematic maps reveal that ~14 % (~217 km2) of basin area falls under very good, ~32 % (~486 km2) under good, ~23 % (~353 km2) under moderate, and 30 % (~443 km2) under poor zones for groundwater potential. From the sub-basin-wise prioritisation, it has been inferred that SB-III scored highest groundwater potential, followed by SB-X. Result of morphometric analyses with the hydrologic parameters indicates that ~99 % area of SB-III and SB-X are under very good to moderate groundwater potential zone. This study clearly demonstrates that hydrological parameters in relation with morphometric analyses are useful to demarcate the prospect zones of groundwater.

Geomorphology and drainage characteristics of the Gurpur river basin have been studied using sate... more Geomorphology and drainage characteristics of the Gurpur river basin have been studied using satellite images, topographic maps and geographic information system (GIS) techniques. Geomorphology and morphometric parameters have been used to prioritize the sub-basins (SB-I to -VII) and identify the most deficit/surplus zones of groundwater. The study reveals that 8% (SB-VII) to 85% (SB-II) area of the geomorphic units have poor to moderate groundwater prospect. About 16% (SB-V) to 92% (SB-VII) area were estimated as good to excellent zones for groundwater potential. Bifurcation ratio results show that geomorphic control predominates over structural control in the development of drainage network. Computed values of stream frequency of SB-II, SB-III and SB-VI indicate steep ground slopes, with less permeable rocks, while drainage density indicates that the river basin is moderately permeable. Sub-basin-wise prioritization reveals that SB-II is the most deficit zone, while SB-VII is found to be surplus zone of groundwater potential.

The biophysical effects of a storm in the most oligotrophic waters of the South Indian Ocean (SIO... more The biophysical effects of a storm in the most oligotrophic waters of the South Indian Ocean (SIO) subtropical gyre have been investigated by conjunctive analyses using space-borne sensors and in situ observations. The most oligotrophic waters of the SIO are identified using more than 8-years of chlorophyll-a images derived from Aqua-Moderate Resolution Imaging Spectroradiometer (Aqua-MODIS). Earlier studies revealed that the source of oceanic primary production enhancement in these oligotrophic waters has remained inconclusive. However, the present study succeeded in attributing the cyclone, named Edzani, which passed over these waters and to be responsible for enriching the chlorophyll-a pigment, lowering of sea surface temperature (SST) and deepening of mixed layer. Analyses of MODIS Chlorophyll-a and SST images during the cyclone and pre-cyclone period shows lowering of SST values up to 2.23 °C and chlorophyll-a enrichment up to 0.062 mg/m3 from the pre-storm values along the cyclone track. Argo floats in the region recorded 10 m deepening of mixed layer with an average mixed layer cooling of ∼1.34 °C and 0.14‰ increase in salinity. These changes controlled by the physical processes have been examined using wind stress, wind stress curl and upwelling velocity derived from the new Advanced Scatterometer (ASCAT). The results provide a significant evidence to suggest that the frequent storms could possibly modify the prevailing oligotrophic conditions of the SIO subtropical gyres into a relatively productive environment, thus leading to regulate the global carbon cycle which is an essential component of climate change.

The Egyptian Journal of Remote Sensing and Space Sciences (Elsevier), Jun 2012

"""Satellite data product validation and algorithm development activities both require the subst... more """Satellite data product validation and algorithm development activities both require the
substantial accumulation of high-quality in situ observations. Data were acquired from Ocean Colour
Monitor (OCM) and in situ observations for tuning of Tassan’s algorithm (Tassan, 1994) to
retrieve the suspended sediment concentration (SSC) in the coastal waters off southern Karnataka,
India. Tassan’s algorithm has been modified regionally by adopting statistical/graphical criteria to
characterize the spatial and seasonal distribution of SSC. A concurrent and collocated datasets
(n= 120) of in situ SSC and OCM based remote sensing reflectance [Rrs(k) in bands 490, 555
and 670 nm] were regressed. The linear fit yielded regionally tuned new coefficients which were
replaced in place of Tassan’s global coefficients. The tuned algorithm was shown to retrieve SSC
with range of 1.1–37.12 mg/l, which means it can be used for coastal waters. Since in situ samples
were collected within the continental margin (average depth of 20 m), we retain the global SSC
algorithm (Tassan, 1994) approach for deeper bathymetric values (>50 m depth) where we have
no in situ measurements. Comparative analysis indicated statistically significant relationship
(R2 =0.99; n= 45; p< 0.05 at 95% confidence level) between in situ SSC and regionally
tuned algorithm based SSC, with bias of 0.36 mg/l and root mean square (RMS) difference of
0.73 mg/l. This result clearly demonstrated the improvement of SSC measurement from OCM using regionally tuned Tassan’s algorithm (RMS= 0.73 mg/l) over the globally coefficient based Tassan’s
algorithm (RMS= 16.1 mg/l).
The tuned regional algorithm was used to estimate SSC in 2004, 2005 and 2007 which shows the
concentration varied from 1.13 to 28.1 mg/l in 2004, 1.84 to 23.12 mg/l in 2005 and 2 to 27.85 mg/l
in 2007. Graphical and statistical methods using analysis of variance (ANOVA) have shown significant
seasonal variability and inter-station spatial variability in SSC. Peak concentrations were
recorded in the post-monsoon followed by the pre-monsoon period. The wind, wave and current
pattern associated with southwest monsoon possibly controls the seasonal distribution, while nearshore
turbulence and littoral transport influence the spatial distribution. This paper clearly demonstrated
the potential application of regionally tuned algorithm for SSC mapping to study the spatial
and seasonal pattern in shallow water off southern Karnataka.
"""

http://www.tandfonline.com/doi/full/10.1080/10106049.2010.496004#.UZtJd6wrz5M, Jul 2010

The Netravati and Gurpur (N–G) river basins are tectonically active due to a number of seismicall... more The Netravati and Gurpur (N–G) river basins are tectonically active due to a number of seismically active faults/lineaments and their proximity to Mulki–Pulicat Lake axis. The gradient of the river channels has gradually reduced (after 10 km from their origin) and has forced the rivers to flow slowly in meandering and zigzag paths. The nature and intensity of meanders are governed by geological and tectonic conditions of the river basins. Significant changes in river channels, between the years 1910 and 2005, have been detected in three blocks – Block-I (Netravati) and Blocks-II and III (Gurpur) – and studied in detail by comparing topographic maps with Indian Remote Sensing Satellite, LISS-III images through GIS techniques. The block-wise qualitative and quantitative changes of these channels indicate that they are narrowed and migrate towards south due to neotectonic activities, formation of braided islands, variation in flow intensity and anthropogenic interventions like construction of vented dams and sand mining.

The 560-km-long Kerala coast is characterised by long barriers with narrow beaches and steep clif... more The 560-km-long Kerala coast is characterised by long barriers with narrow beaches and steep cliffs. Distribution of cliffs from nine sections measuring a cumulative length of 63.5 km is evaluated in ArcGIS Software using topomaps and field survey data. The cliff sections in the southern coast comprise both permeable and impermeable rocks, whereas those along northern coast are comprised of either Precambrian crystalline and/or Tertiary formations. Notches, caves and even small arches are developed in Cannanore, Dharmadam and Kadalundi cliffs, where only primary laterites are exposed to wave attack. Stacks composed of laterite and Precambrian crystallines found in nearshore of cliffed coast indicate recession of shoreline. Mass wasting, mudslide and mudflow type of cliff failures are common in permeable to semi-permeable rocks, whereas rotational sliding, rockfall and toppling failure are found in hard rock cliffs. Retreat of cliff sections are induced by natural or anthropogenic activities or both. Rate of recession vary from a few centimetres to one metre/year depending upon the nature of lithology, structures and recession agents acting upon the cliffs. Various methods of cliff protection for e.g. hard structures—revetments, groins, seawalls, breakwater and jetties—and soft measures—artificial reefs/marsh creation, floating breakwaters, beach nourishment, beach scraping and vegetation planting—are suggested.