Ekman revisited: Surface currents to the left of the winds in the Northern Hemisphere.

Ekman's theory of wind-driven ocean currents on a rotating planet is central to our understanding of why surface currents are deflected to the right of the winds in the Northern Hemisphere and to the left of the winds in the Southern Hemisphere. The theory admits solutions for currents deflected in the opposite direction at periods shorter than the local inertial period, but Ekman did not mention these currents, and they have only rarely been observed. Here, we describe a prominent example of surface flow in the Bay of Bengal directed to the left of clockwise-rotating land breeze wind forcing using multiple years of data from a long-term deepwater surface moored buoy.

Turbulent characteristics of momentum flux in the marine atmospheric boundary layer of North Bay of Bengal.

We use a 16-month-long, 20 Hz wind data from a mooring deployed in the Bay of Bengal (BoB) to study the characteristics of turbulent wind stress ( events in the marine atmospheric boundary layer (MABL). Quadrant analysis of the motion-corrected and suggests that sweep and ejections, representing downward stress transfer into the ocean, dominate the (~ 140%). In comparison, outward and inward interactions representing an upward stress transfer into the atmosphere provide the counter-contribution (~ 40%).

Dynamics of subsurface chlorophyll maxima in the northern Indian Ocean.

Subsurface chlorophyll maxima (SCM) significantly contributes to oceanic primary productivity, emphasizing the need to study its dynamics and governing mechanisms. We used datasets from various platforms to investigate relationships between the SCM characteristics (SCM depth (Z), SCM magnitude (Chl), SCM thickness (T)) and environmental variables modulated by various physical processes in the Northern Indian Ocean (NIO). In the Arabian Sea (western NIO), seasonal processes like convective mixing and upwelling, primarily regulated the SCM characteristics.

Chromophoric dissolved organic matter traces seasonally changing coastal processes in a river-influenced region of the western Bay of Bengal.

The optical characteristics of colored dissolved organic matter (CDOM) serve as a convenient tool for evaluating coastal processes, e.g., river runoff, anthropogenic inputs, primary production, and bacterial/photochemical processes.

Investigating Indian oil sardine aggregation events in coastal waters of the southeastern Arabian sea.

The southwest coast of India experiences frequent Indian oil sardine (IOS) nearshore aggregation events, especially in the coastal waters off Kerala. These ephemeral dense IOS aggregation events are known as "Sardine Run". To investigate the reason and provide a scientific basis for these sporadic events, satellite/model-derived physical, meteorological, and biological parameters were analysed.

Extraction of persistent lagrangian coherent structures for the pollutant transport prediction in the Bay of Bengal.

Lagrangian Coherent Structures (LCS) are the hidden fluid flow skeletons that provide meaningful information about the Lagrangian circulation. In this study, we computed the monthly climatological LCSs (cLCS) maps utilizing 24 years (1994-2017) of HYbrid Coordinate Ocean Model (HYCOM) currents and ECMWF re-analysis winds in the Bay of Bengal (BoB). The seasonal reversal of winds and associated reversal of currents makes the BoB dynamic.

Sea-surface pCO maps for the Bay of Bengal based on advanced machine learning algorithms.

Lack of sufficient observations has been an impediment for understanding the spatial and temporal variability of sea-surface pCO for the Bay of Bengal (BoB). The limited number of observations into existing machine learning (ML) products from BoB often results in high prediction errors. This study develops climatological sea-surface pCO maps using a significant number of open and coastal ocean observations of pCO and associated variables regulating pCO variability in BoB.

Impact of bathymetry on Indian Ocean circulation in a nested regional ocean model.

The Regional Indian Ocean model based on Modular Ocean Model (MOM4p1) was used to understand the importance of a realistic representation of bathymetry on Ocean General Circulation. The model has 1/4° uniform horizontal resolution and is forced with Coordinated Ocean-Ice Reference Experiments (CORE-II) inter-annual forcing with two simulations named BLND (realistic bathymetry) and OM3 (smoothed bathymetry), which only differ in the representation of bathymetry for the years 1992-2005. We also used recent reanalysis products from ORAS5 and SODA3 and ADCP observation to compare the subsurface currents.

Major sources of sinking particulate organic matter in the western Bay of Bengal.

Impacts of river discharge on coastal ocean processes are multi-dimensional. Studies on sinking particle fluxes, composition and their seasonal variability in coastal oceans are very limited. In this study, we investigated the impact of river discharge on seasonal variability in sinking fluxes of total mass, biogenic and lithogenic material in a river-dominated continental margin, western coastal Bay of Bengal.

An integrated buoy-satellite based coastal water quality nowcasting system: India's pioneering efforts towards addressing UN ocean decade challenges.

The Indian coastal waters are stressed due to a multitude of factors, such as the discharge of industrial effluents, urbanization (municipal sewage), agricultural runoff, and river discharge. The coastal waters along the eastern and western seaboard of India exhibit contrasting characteristics in terms of seasonality, the magnitude of river influx, circulation pattern, and degree of anthropogenic activity. Therefore, understanding these processes and forecasting their occurrence is highly necessary to secure the health of coastal waters, habitats, marine resources, and the safety of tourists.

Water column properties associated with massive algal bloom of green Noctiluca scintillans in the Arabian Sea.

An algal bloom of Noctiluca scintillans (NS) was monitored for 20 days in the Arabian Sea during February 2017. The stations under the influence of NS had low temperature and high salinity compared to outside indicating influence of convective mixing. The microscopic cell count of NS reached a value of 52,600 cells l.

Implications of seismic and GNSS strain rates in Himachal, Kashmir and Ladakh.

We report the present day GNSS velocities (2015-2021) and strain rates in Himachal, Kashmir and Ladakh Himalaya covering the rupture zones of the 2005 Muzaffarabad earthquake and the 1905 Kangra earthquake. Geodetic strain rates estimated from GPS velocities of about 58 sites spanning last two decades of measurements indicate a mean compression rate of - 32.5 ns/year (nanostrain/year) and dilatation of - 37.

Recent global increase in multiple rapid intensification of tropical cyclones.

The rapid intensification (RI ≥ 30 knots/24-h) of tropical cyclones (TCs) makes TC forecasting difficult, resulting in severe damage to property and life. Forecasting can get even worse if TCs have experienced RI more than once (referred to as "multiple-RI TCs") in their lifetime. On a global scale, the relation between long-term trends of multiple-RI TC frequency and maximum potential intensity (MPI) changes is investigated in this study.

Real-time quality control of optical backscattering data from Biogeochemical-Argo floats.

Background: Biogeochemical-Argo floats are collecting an unprecedented number of profiles of optical backscattering measurements in the global ocean. Backscattering (BBP) data are crucial to understanding ocean particle dynamics and the biological carbon pump. Yet, so far, no procedures have been agreed upon to quality control BBP data in real time.

Status and conservation challenges of the second-largest seagrass bed in India: Chilika lagoon.

Studies related to seagrass ecology, conservation, and management are sparse and highly biased in India. Even though the geographical distribution of seagrass is diverse in India, about 74% of the scientific publications have been made from Palk Bay and the Gulf of Mannar from Tamilnadu. Chilika, the largest lagoon in Asia, harbors the second largest seagrass meadow in India 22% of the total.

Recent changes in atmospheric input and primary productivity in the north Indian Ocean.

Global oceanic regions are rapidly changing in terms of their temperature, oxygen, heat content, salinity and biogeochemistry. Since the biogeochemistry of the oceans is important and pivotal for global food production, and a major part of the world population relies on marine resources for their daily life and livelihood, it is imperative to monitor and find the spatio-temporal changes in the primary productivity of oceans. Here, we estimate the changes in Chlorophyll-a (Chl-a) and Net Primary Productivity (NPP) in the north Indian Ocean (NIO) basins of Bay of Bengal and Arabian Sea for the period 1998-2019.

Quantifying the role of antecedent Southwestern Indian Ocean capacitance on the summer monsoon rainfall variability over homogeneous regions of India.

The role of ocean variability is at a focal point in improving the weather and climate forecasts at different spatial and temporal scales. We study the effect of antecedent southwestern Indian Ocean mean sea level anomaly (MSLA) and sea surface temperature anomalies (SSTA) as a proxy to upper ocean heat capacitance on all India summer monsoon rainfall (AISMR) during 1993-2019. SSTA and MSLA over the southwestern Indian Ocean (SWIO) have been influenced by El Niño-Southern Oscillation (ENSO), the impact of ENSO-induced SWIO variability was low on rainfall variability over several homogeneous regions.

A high concentration CO pool over the Indo-Pacific Warm Pool.

Anthropogenic emissions have produced significant amount of carbon dioxide (CO) in the atmosphere since the beginning of the industrial revolution. High levels of atmospheric CO increases global temperature as CO absorbs outgoing longwave radiation and re-emits. Though a well-mixed greenhouse gas, CO concentration is not uniform in the atmosphere across different altitudes and latitudes.

Observational evidence of salt finger in the diurnal thermocline.

Due to strong turbulent mixing, the ocean surface boundary layer region is generally not conducive to double diffusion. However, vertical microstructure profiles observations in the northeastern Arabian Sea during May 2019 imply the formation of salt fingers in the diurnal thermocline (DT) region during the daytime. In the DT layer, conditions are favorable for salt fingering: Turner angle values are between 50 and 55° with both temperature and salinity decreasing with depth; shear-driven mixing is weak with a turbulent Reynolds number of about 30.

Effects of tidal cycle on greenhouse gases emissions from a tropical estuary.

The potential effects of tidal and diel cycles on fluxes and concentrations of carbon dioxide (pCO), methane (CH), and nitrous oxide (NO) along with associated biogeochemical processes remain poorly understood in tropical estuaries. The present study, based on six-hourly sampling for nine consecutive days at three locations along the salinity gradient in the Mahanadi estuary of India, revealed that the tidal forcing affected pCO and CH in the mixing zone with elevated concentrations during low tide with maximum concentrations up to 21,606 μatm and 285 μM, respectively. pCO increased with decrease in tidal height within low and high tide duration as well, possibly due to higher relative contribution of freshwater with high CO.

Wave induced coastal flooding along the southwest coast of India during tropical cyclone Tauktae.

The coastal flood during the tropical cyclone Tauktae, 2021, at Chellanam coast, Kerala, India, has invited wide attention as the wave overtopping severely affected coastal properties and livelihood. We used a combination of WAVEWATCHIII and XBeach to study the coastal inundation during high waves. The effect of low-frequency waves and the rise in the coastal water level due to wave setup caused the inundation at Chellanam, even during low tide with negligible surge height.

Spatial and seasonal trends of trace metals in the surficial sediments from off Kochi - Geochemistry and environmental implications.

Fifty four sediment samples representing pre and post-monsoon seasons were collected along a transect from off Kochi, lying between the latitudes 9°57'59.5″-9°54'30.4″ and longitudes 76°11'7.

Exploring the impact of southern ocean sea ice on the Indian Ocean swells.

The present study analyzes the impact of the Southern Ocean (SO) sea ice concentration on the north Indian Ocean (NIO) wave fields through swells using 6 years (2016-2021) of WAVEWATCH III (WWIII) simulations. We did two experimental runs of WWIII, one with sea ice concentration and winds as the forcing (W3) and the second run with only wind forcing (W3). Analysis shows the impact of the SO sea ice concentration on northward swell peaks in September-November, coinciding with the maximum sea ice extent in the Antarctic region of the Indian Ocean.

Role of tide and lunar phases on the migration pattern of juvenile Hilsa shad (Tenualosa ilisha) within a meso-macrotidal estuary.

Tide and lunar phases often influence the behaviour and life cycle of different fishes, especially migratory species. In the Hooghly River estuary, Hilsa shad is an anadromous fish species that migrates from the adjacent sea to the estuary and rivers for spawning. After spawning, the juveniles remain in the rivers and estuary for few months then start their downstream migration towards the adjacent sea.

Response of coastal phytoplankton pigment composition to tropical cyclone Fani.

Phytoplankton pigment composition was evaluated during the pre-cyclone phase (PRCP) and post-cyclone phase (POCP) of tropical cyclone Fani in the coastal waters of the northwestern Bay of Bengal. The chromatographic analysis revealed higher pigment diversity and an increase in individual pigment concentration during POCP. Chlorophyll-a (chl-a) was the dominant pigment during PRCP and POCP, followed by fucoxanthin.