Strong Upwelling Research Articles

Unprecedented Surface Chlorophyll Blooms in the Southeastern Arabian Sea During an Extreme Negative Indian Ocean Dipole

AbstractObservations of ocean color in the southeastern Arabian Sea (SEAS) during the late boreal summer and fall of 2016 reveal the highest surface chlorophyll concentrations (>1.0 mg m−3) ever reported in the region in the past two decades of the satellite era. Anomalous chlorophyll blooms were triggered by two cold‐core eddies, along the periphery of the coastal upwelling zone. Observational evidence suggest that the eddy formation and propagation can be attributed to the local wind forcing and the remote effects originating around Sri Lanka and the southern tip of India (STI) during the extreme negative Indian Ocean Dipole (IOD) of 2016. The eddy‐induced anomalous shoaling of thermocline indicates strong upwelling of subsurface nutrients and chlorophyll and enhanced light availability for phytoplankton growth favoring the observed biological response. The study signifies the unprecedented impacts of extreme climatic events on oceanic chlorophyll and the need for better understanding of the associated biophysical interactions.

The classification of upwelling indicators base on sea surface temperature, chlorophyll-a and upwelling index, the case study in Southern Java to Timor Waters

The Understanding of the existence of upwelling, which concerning location, onset and ending, top temporally, strength, extent area are very important for the management of marine waters, especially fishing and conservation. A method is needed to identify the area of upwelling base on its indicators. The one method that is needed is to classify the upwelling indicator. The aim of the research is fist studying the method classification of upwelling criteria base on SST, chlorophyll-a and upwelling index. Second, apply classification of upwelling criteria for mapping upwelling area on four case climate variability and third examine the effect of ENSO and IOD on the variability of the upwelling area. The research result, based on SST, chlorophyll-a and upwelling index in the Indian Ocean south of Java to Timor with statistical methods, have successfully divided upwelling criteria into 4: weak upwelling, medium upwelling, strong upwelling and very strong upwelling. Based on the upwelling criteria, we can apply mapping the location of upwelling, to determine the spatial distribution and extent of upwelling in Indian Ocean waters southern of Java to Timor. Two indicators of upwelling SST and chlorophyll-a are more accurate in the application if be used together. The variability of ENSO and IOD significantly effected growing and reducing the range of upwelling indicator (SST, chlorophyll-a and upwelling index), but the IOD index much greater effecting than ENSO index (SOI).

Contrasting effects of coastal upwelling on growth and recruitment of nearshore Pacific rockfishes (genus Sebastes)

Knowledge of processes underlying recruitment is critical for understanding marine population dynamics and their response to ocean climate. We investigated the relationship between coastal upwelling and early life history of black rockfish (Sebastes melanops), a midwater aggregating species, and CQB rockfishes (a solitary benthic species complex including Sebastes caurinus, Sebastes maliger, and Sebastes auriculatus), between two oceanographically distinct years on the west coast of Vancouver Island, Canada. We analysed otolith microstructure to determine parturition and settlement dates, pelagic durations, and pre- and postsettlement growth rates. High CQB rockfish recruitment in 2005 was associated with prolonged downwelling and warm ocean temperatures, late parturition dates, fast presettlement growth, short pelagic durations, and small size-at-settlement. In contrast, high black rockfish recruitment in 2006 was associated with strong upwelling and cool ocean temperatures, slow presettlement growth, and protracted pelagic durations. Presettlement growth of both rockfish complexes increased with high sea surface temperature, but was unrelated to chlorophyll a concentration. Our results indicate that the same oceanographic conditions give rise to fast presettlement growth and short pelagic durations for both groups, but that different factors lead to strong recruitment in each.

Spawning ecology of the European anchovy (Engraulis encrasicolus) in the Strait of Sicily: Linking variations of zooplankton prey, fish density, growth, and reproduction in an upwelling system

A 12-year time series (2005–2016) was examined to explore relationships between European anchovy density, growth, reproduction and habitat dynamics in an upwelling system. Specifically, data used for a daily egg production method were combined with oceanographic data, prey availability, as well as acoustic surveys of the anchovy stock in the Strait of Sicily, in the Central Mediterranean Sea. Variables typically used for evaluating habitat dynamics (i.e. water temperature, chlorophyll-a, zooplankton concentration, kinetic energy, mixed layer depth and upwelling index) indicated strong upwelling events during the summer, when anchovy spawns. A linear ‘principal component’ combination of environmental traits, associated with summer upwelling, was identified by step-wise regression as a driver for growth (length at the end of the first year; L1), reproductive investment (gonad-somatic index; GSI), as well as egg production (daily specific fecundity; DSF). These relationships are consistent with direct energy flow from the environment to both somatic growth and reproductive output, indicating an income breeding strategy by anchovy (i.e. surplus energy acquired during the summer breeding season is used directly for reproductive growth). Step-wise regression also identified three additional relationships: (1) a density-dependent mechanism reducing growth (L1) and fecundity (DSF) at higher fish densities; (2) higher fish condition (Kn) positively affecting growth (L1); (3) higher prey availability (mesozooplankton concentration) positively affecting GSI. This time series and approach are promising for exploring the abiotic and biotic mechanisms setting year class strength in advance of recruitment to the fishery.

Upwelling characteristics and nutrient enrichment of the Kangaroo Island upwelling region, South Australia

An analysis is presented of hydrographic and nutrient data collected over three years for the Kangaroo Island upwelling region, Lincoln Shelf, South Australia, to determine the signature of upwelled water, depth of upwelling and the source water mass being brought onto the shelf. Strong upwelling seasons were recorded during the 2007–2008 and 2009–2010 summers, while the summer of 2008–2009 had only one weak upwelling event. Strong upwelling events during February and March 2008 and February and March 2010 recorded temperatures and salinities as low as 10.4°C and 34.85, and NOx and phosphate concentrations as high as 13.35 and 0.94 μmol/L, respectively, at 105 m on the shelf. Upwelled water properties matched slope water properties between 240 and 370 m, indicating water can be upwelled over depths of 200 m or more. Upwelling from these depths sources South Australian Basin Central Water of Southern Ocean origin, which is transported west along the slope by the Flinders Current System. New results for nutrients show average values of NOx and phosphate during months of strong upwelling to be 6.1 times and 4.6 times greater, respectively, than during winter months, and that upwelled water can have nutrient concentrations up to 90 times higher than those in summer surface waters. Strong relationships between temperature and nutrients on the slope can help estimate nutrient concentrations supplied to the shelf during upwelling events. Upwelled water was also low in silicate, a signature of Southern Ocean water masses, which has implications for phytoplankton community structure and diatom abundance on the shelf.

Return of the “age of dinoflagellates” in Monterey Bay: Drivers of dinoflagellate dominance examined using automated imaging flow cytometry and long‐term time series analysis

AbstractPhytoplankton biomass in Monterey Bay, California is typically dominated by diatoms, but it shifted to dinoflagellates twice in the past 18 years (2004–2007, 2017–2018), which was associated with increased harmful algal blooms. Located within the central California Current System (CCS), Monterey Bay is strongly influenced by cycles of upwelling‐favorable winds and their relaxation or reversal. Both dinoflagellate‐dominated periods were linked to a negative North Pacific Gyre Oscillation (NPGO) and increased river discharge, but each had a different relationship with upwelling. To examine the connection between large‐scale and local forcings underlying floristic shifts in the phytoplankton assemblage, an Imaging FlowCytobot (IFCB) was deployed within the Monterey Bay upwelling shadow for a full year. A machine learning classifier differentiating IFCB images of the phytoplankton assemblage was developed. Despite anomalously strong upwelling in 2018, dinoflagellates comprised 57% of the annual phytoplankton‐specific biomass. During upwelling, dinoflagellates appear to have accumulated at convergent fronts, while during relaxation these frontal populations were transported to the nearshore where they seeded local blooms. Frequent upwelling‐relaxation cycles and local wind anomalies generated an unusually retentive circulation pattern in the upwelling shadow, producing a warm and stratified bloom incubator. Thus, local features and forcings (upwelling shadow, winds, river discharge) modified the effects of regional‐ and basin‐scale oceanographic variability (regional upwelling, NPGO), altering local phytoplankton patterns. As North Pacific decadal variability and CCS upwelling intensity increase under climate warming, dinoflagellates may become more common in some CCS regions, due to the enhancement or mitigation of large‐scale trends by local forcings.

Strong upwelling conditions drive differences in species abundance and community composition along the Atlantic coasts of Morocco and Western Sahara

Upwelling strongly influences the composition and dynamics of coastal communities by affecting species abundances, recruitment, dispersal and distribution. Coastal upwelling areas are key model regions to study the responses of coastal species to climate change because they are characterized by cooler water conditions and experience lower warming rates than adjacent regions, making them effective ‘control’ or refuge sites. This is particularly true for the benthic species of rocky shores in upwelling areas because they are sedentary, inhabit the interface between marine and terrestrial habitats, are exposed to extremely severe and variable environmental conditions and often live near their tolerance limits. We sampled roughly 2000 km of the Atlantic coast of Morocco and Western Sahara to assess the influence of upwelling cells on patterns of diversity and abundance of northern African rocky shore species. We recorded 186 taxa, providing clarification of the distribution of 141 algae and documenting nine new species records for Morocco and Western Sahara. The results emphasize the influence of upwelling on the abundance and distribution of these organisms. The contrast between non-upwelling and upwelling areas highlights the direct and indirect importance of water temperature in shaping these communities, pointing to the consequences of large-scale warming. Such warming is likely to threaten intertidal species that already live close to their thermal tolerance limits and are not buffered by the effects of upwelling.

Barium isotope systematics of subduction zones

Subduction zones are the focal points of mass transfer between the surface and deep Earth. Despite their significance, there remains substantial debate regarding the specific mechanisms of material transport from the slab to the overlying magmatic arc. Broadly, models accounting for slab material transport focus on the relative sequence of events promoting arc volcanism and, in particular, whether mobilization of the down-going slab leads or lags mixing with the mantle wedge. To address these uncertainties, we outline the utility of barium (Ba) isotope mass balance in subduction zones as a means to test different slab material transport models. Barium is a highly fluid-mobile element that is significantly enriched in arc magmas and is thus thought to be a sensitive tracer of slab material transport in arcs.We also present qualitative Ba isotopic mass balances for two well-characterized subduction zones—the Aleutian and Ryukyu magmatic arcs—by analyzing the Ba isotope systematics of their respective subduction inputs and outputs. Despite the narrow (and similar) Ba-isotope range of slab inputs to both systems, we find that erupted magmas exhibit systematic variations indicative of a small negative isotope fractionation during Ba mobilization (≈20–40 ppm AMU−1). We suggest that AOC (altered oceanic crust) is not the principal source of these negative isotope values using other geochemical parameters (e.g., Rb/Ba, Pb isotopes), and infer that the Ba isotope composition of AOC—though contributing a minor amount of Ba in these systems—is isotopically heavier than the overlying sediment package and the depleted mantle. Altogether, these findings are significant as they indicate that the magnitude of isotope fractionation associated with Ba mobilization is small relative to the likely isotopic contrast between subduction inputs in other subduction zones, such as beneath areas of strong ocean upwelling (e.g., South Sandwich, Kamchatka). Thus, we propose that the Ba isotope composition of erupted arc magmas holds great promise for constraining the importance of different slab components, which could help address uncertainties regarding the mechanism of slab material transport in subduction zones.

First Synoptic Observations of Geomagnetic Storm Effects on the Global‐Scale OI 135.6‐nm Dayglow in the Thermosphere by the GOLD Mission

AbstractThe Global‐scale Observations of the Limb and Disk (GOLD) mission provides, for the first time, a synoptic view of the thermospheric response to a moderate geomagnetic storm at a 30‐min cadence. The observations showed that the OI 135.6‐nm emission substantially decreased at middle and high latitudes, but it increased at low latitudes. The depletion pattern between 4 and 6 November 2018 was likely due to the strong upwelling of the high‐latitude thermosphere. The deepest depletion in brightness that occurred near local noon was of ~300–400 R (~35% of the quiet time background level) and displayed a striking westward movement. First‐principles modeling reasonably reproduced the overall morphology of brightness response to the geomagnetic storm despite the depletion magnitude in brightness being underestimated. The postprocessing of the simulation results revealed that the westward movement of the deepest depletion was attributable to the horizontal wind changes driven by the geomagnetic storm.

Relationship Between the Spatiotemporal Distribution of Dominant Small Pelagic Fishes and Environmental Factors in Mauritanian Waters

The relationship between the spatiotemporal distribution of three dominant small pelagic fishes, including chub mackerel (Scomber japonicus), horse mackerel (Trachurus trecae) and round sardinella (Sardinella aurita), and the environmental factors in Mauritanian waters were analyzed by using 4 years of logbook data of commercial purse seine fisheries to improve the efficiency of fishery and management of sustainable exploitation. A Tweedie-generalized additive model (GAM) of 8-day average catches and the monthly geostatistical analysis of daily catches were used in this study to analyze the influence of environmental factors on catch per unit of effort (CPUEs) and to map the spatial distribution of three mixed dominant small pelagic fishes, respectively. A 10′ × 10′ grid was used, and environmental factors were processed from remote sensing, including 8-day average sea surface temperature (SST), the nearest distance between SST fronts and CPUE position (Df), chlorophyll-a (Chl-a) concentration, salinity, and eddy kinetic energy. Results showed that 1) the distribution of three dominant small pelagic fishes might be related to the intensity of upwelling in Mauritanian waters; 2) oceanic fronts might play a key role in the ecology of chub mackerel, horse mackerel, and round sardinella; 3) Chl-a concentration might be associated with the feeding grounds of chub mackerel; 4) the target species distribution appeared sensitive to gradient changes in the amount of salinity; 5) three zones (northern, central, and southern) with variable abundances were delineated; and 6) a high concentration of the center of gravity in the central zone might be related to the strong upwelling of nutrient-rich waters. This study can provide new insights to enhance the fishery efficiency and sustainable exploitation management of purse seiners in certain area off Mauritania.

Seasonal and synoptic oceanographic changes influence the larval biodiversity of a retentive upwelling shadow

Understanding sources of variability in larval supply and transport is integral to the dynamics, structure and effective management of marine populations and communities. Yet, a barrier to this understanding is the high variability in the supply and transport of marine larvae, especially in upwelling regions where wind forcing causes dynamic circulation. Since larvae of many species complete development close to shore, resolving the relationship between oceanographic processes and nearshore larval assemblages is essential to better understand larval transport in highly productive upwelling regions. The goal of our study was to examine the effects of variation in upwelling and relaxation dynamics on the nearshore larval assemblage in northern Monterey Bay. To determine how seasonal and daily upwelling and relaxation dynamics influence the nearshore larval assemblage, we surveyed distributions of marine larvae and physical, environmental factors along a cross-shelf transect in northern Monterey Bay, USA, during August and October of 2013.Conditions in August and October differed in temperature, salinity, stratification, and chlorophyll-a fluorescence. Richness and diversity of the larval assemblage did not change appreciably, but the abundance and composition of species shifted after the influx of offshore waters. Specifically, nearshore taxa were more abundant during August, which was characterized by strong upwelling conditions, and especially more abundant with increased wind forcing leading to a retentive upwelling shadow in the northern bay. Conversely, offshore taxa were more abundant during October, which was characterized by weakened upwelling and the persistent influx of offshore water. Our study suggests that relationships between larval taxa, life history characteristics, and water types provide insights into water mass history, circulation and larval recruitment in highly dynamic upwelling regions.

Variability of bottom carbonate chemistry over the deep coral reefs in the Florida Straits and the impacts of mesoscale processes

Abundant and diverse cold-water coral and fish communities can be found in the deep waters of the Florida Straits, which are believed to be living under suboptimal conditions impacted by increasing oceanic CO2 levels. Yet, little is known regarding the spatial–temporal variability of bottom carbonate chemistry parameters and their dynamic drivers in this area. To address this issue, we present results from numerical simulations of a coupled physical-biogeochemical model for the south Florida shelf and Florida Straits. Our exploratory analysis focuses on two well-known deep-coral habitats: Pourtalès Terrace (200–450 m) and Miami Terrace (270–600 m). Results suggest that bottom waters along the northern/western slope of the Straits are comprised primarily of the North Atlantic Central Water (NWCW) and Antarctic Intermediate Water (AAIW), driven by upwelling associated with the bottom Ekman transport of the Florida Current. Over the Pourtalès Terrace, both the meandering of the Florida Current and mesoscale eddies modulate the upwelling (downwelling) of cold (warm) waters. In contrast, Florida Current makes a sharp turn at the southern end of the Miami Terrace leading to persistent island wakes, frequent occurrences of a transient eddy, and strong upwelling of deep waters toward the platform of the terrace. Passage of the transient eddy often accompanies strong downwelling of warm waters and a return (southward) flow on top of the platform. Overall, bottom water properties including temperature (T), dissolved inorganic carbon (DIC) and total alkalinity (TA) show strong variability on weekly to monthly time-scales over entire Pourtalès Terrace and on the platform of Miami Terrac, mostly driven by physics. In deeper areas (>400 m), bottom water properties are fairly stable with both DIC and TA showing narrow ranges. Interestingly, waters over the southeastern portion of the Pourtalès Terrace show consistently warmer temperature, lower DIC, and higher TA than those on top of this terrace. The aragonite saturation state (Ω) ranges 1.2-2 on top of the Pourtalès Terrace and 1.2-1.7 both on top of Miami Terrace and on the upper slope of Pourtalès Terrace. In the deeper slope areas (>400 m), it is nearly constant at 1.2-1.3. This modeling effort suggests that remote forcing and biogeochemical processes along the transport paths, from the Gulf of Mexico to the Straits, are significant but second-order contributors to the variability of bottom carbonate chemistry. The impacts of benthic biogeochemical processes along the transit paths are not resolved.

Satellite Evidence of Upper Ocean Responses to Cyclone Nilofar

ABSTRACTCyclone Nilofar was the third-strongest cyclone in the Arabian Sea. It was a category 4 cyclone that arrived in last week of October 2014. It lingered in the Arabian Sea for 10 days and caused a significant phytoplankton bloom that was detected by satellite observation. In this study, the authors investigated the ocean biological and physical responses to cyclone Nilofar using chlorophyll a (chl a) concentration, sea surface temperature (SST), sea surface height anomaly (SSHA), sea surface wind measurements derived from different satellites, and in situ data. The maximum chl a concentration (>3.34 mg m−3) increased about 28 times in the Arabian Sea after the passage of the cyclone in comparison with the chl a concentration (0.12–0.92 mg m−3) before the passage of cyclone. Using the relationship of wind stress curl and upwelling, the authors found that during the cyclone the speed of upwelling increased more than 18 times compared with the speed in the period before the cyclone. Moreover, the mixed layer deepened by about 40 m. These findings reveal that the enhancement of chl a concentration was triggered by strong vertical mixing and upwelling. Along the track of the cyclone, the maximum sea surface cooling (4°–5°C) took place in the Arabian Sea along segments A–B and D–F where the translation speed of the cyclone was only 0.9–1.3 m s−1, and the mixed-layer depth was about 10 m in the pre-cyclone period. However, the drop in SST along segment C–D was only 1°–2°C, whereas in the pre-cyclone period the translation speed of the cyclone was 3.1–4.4 m s−1, and the mixed-layer depth was about 25 m in. So, the extent of the SST drop was probably due to the translation speed of the cyclone and the depth of the mixed layer. In addition, the region with the largest decline in SSHA can indicate the location of maximum cooling.

Remotely-sensed L4 SST underestimates the thermal fingerprint of coastal upwelling

Sea Surface Temperature (SST) is an essential variable for understanding key physical and biological processes. Blended and interpolated L4 SST products offer major advantages over alternative SST data sources due to their spatial and temporal completeness, yet their ability to discriminate upwelling-induced steep temperature transitions in coastal waters remains largely unassessed. Here we analysed the performance of eleven L4 GHRSST-compliant products in estimating in situ water temperatures recorded by a large network of shallow subtidal and intertidal temperature loggers deployed in shores covering regimes with a wide range of upwelling intensities. Results indicate that while most products perform satisfactorily for most of the year, performance is severely affected during the upwelling season in locations with strong upwelling. We show that upwelling negatively impacts all four metrics used to assess dataset performance (average bias, correlation, centred root-mean-square error and normalized standard deviation), leading to a considerable overestimation of coastal water temperatures (with average bias exceeding 2 °C in some cases). We also show that while the use of L3 data (i. e., prior to blending and interpolation) leads to an increase in performance compared to L4 GHRSST-compliant products, the gain is probably not substantial enough to offset issues related with their spatial and temporal inconsistency along coastlines. Our results suggest that the use of L4 GHRSST-compliant products can lead to a misrepresentation of the thermal fingerprint of upwelling, and thus should be limited (or even avoided) in locations dominated by its effects. Conversely, the use of L4 GHRSST-compliant products on locations with little to no upwelling appears to be warranted. The mismatch between in situ and remotely-sensed sea water temperatures here reported also highlights the need for implementation of long-term monitoring networks of in situ temperature loggers.

Contrasting assemblages of seabirds in the subglacial meltwater plume and oceanic water of Bowdoin Fjord, northwestern Greenland

AbstractIn Greenland, tidewater glaciers discharge turbid subglacial freshwater into fjords, forming plumes near the calving fronts, and these areas serve as an important foraging habitat for seabirds. To investigate the effect of subglacial discharge on the foraging assemblages of surface feeders and divers in a glacial fjord, we conducted boat-based seabird surveys, near-surface zooplankton samplings, and hydrographic measurements at Bowdoin Fjord, northwestern Greenland in July. Foraging surface feeders (black-legged kittiwake Rissa tridactyla, glaucous gull Larus hyperboreus, and northern fulmar Fulmarus glacialis) aggregated within a plume-affected area in front of Bowdoin Glacier. This area was characterized by highly turbid subglacial meltwater and abundant large-sized zooplankton including Calanus hyperboreus, chaetognaths, and ctenophores near the surface. Surface feeders fed on these aggregated prey presumably transported to the surface by strong upwelling of subglacial meltwater. In contrast, divers (little auk Alle alle, thick-billed murre Uria lomvia, and black guillemot Cepphus grylle) foraged outside the fjord, where turbidity was low and jellyfish and Calanus copepods dominated under the influence of Atlantic water. Our study indicates spatial segregation between surface feeders and divers in a glacial fjord; surface feeders are not hindered by turbidity if taking prey at the surface, whereas divers need clear water.

Distribution of iron in the Western Indian Ocean and the Eastern tropical South pacific: An inter-basin comparison

The Western Indian Ocean (WIO) and Eastern Tropical South Pacific (ETSP) are distinctly different regimes, yet they share several important features. These include a strong upwelling system, a large oxygen minimum zone (OMZ) with active denitrification, a spreading center with extensive hydrothermal activity, and a vast oligotrophic upper water column. Here, we show that the distribution and geochemistry of iron shows remarkable similarities as well. In particular, both basins exhibit large sub-surface plumes of iron derived from sediments underlying the oxygen minimum zones and from hydrothermal sources. Moreover, the behavior of Fe, especially its redox cycling, is remarkably similar in the Arabian Sea and Peruvian oxygen minimum zone, reflecting similar processes associated with the nitrogen cycle in each region. The large Fe plumes under each OMZ are well below the oxygen-free depth, yet they are probably dependent on internal redox cycling and scavenging of Fe within the overlying OMZs. Globally, both the Arabian Sea and Peru margin sediments are hot spots of carbon oxidation, which probably contributes to their importance as Fe sources.The fate of hydrothermally derived Fe in the WIO and ETSP is particularly interesting to compare because their source terms are very different even though their oxidation rates, once they have entered the water column, should be directly comparable. In the ETSP, hydrothermal inputs from along a section of the ultra-fast spreading Southern East Pacific Rise (SEPR) are integrated into a single coherent plume that is exported west across the ocean interior for >4000km. In contrast, hydrothermal inputs to the WIO derive from multiple sources including outflow from the Red Sea via the Gulf of Aden, the Indonesian Throughflow, and from multiple vent-sources along the Carlsbad Ridge, Central Indian Ridge and SW Indian Ridge which are slow, medium and ultra-slow spreading, respectively. As a result, hydrothermally sourced Fe distributions are more complex in the WIO, with several overlapping plumes and distinctly different distributions of two other hydrothermally-derived metals, aluminum and manganese. Here we argue that comparative studies of these basins, with a future emphasis on benthic-water column interactions, will advance knowledge about Fe biogeochemistry and how distributions in the WIO, in particular, are likely to change in the future.

Varying reproductive success under ocean warming and acidification across giant kelp (Macrocystis pyrifera) populations

Understanding how climate change may influence ecosystems depends substantially on its effects on foundation species, such as the ecologically important giant kelp (Macrocystis pyrifera). Despite its broad distribution along strong temperature and pH gradients and strong barriers to dispersal, the potential for local adaptation to climate change variables among kelp populations remains poorly understood. We assessed this potential by exposing giant kelp early life stages from genetically disparate populations in Chile and California to current and projected temperature and pH levels in common garden experiments. We observed high resistance at the haploid life stage to elevated temperatures with developmental failure appearing at the egg and sporophyte production stages among Chilean and high-latitude California populations, suggesting a greater vulnerability to climate- or ENSO-driven warming events. Additionally, populations that experience low pH events via strong upwelling, internal waves, or estuarine processes, produced more eggs per female under experimental low-pH conditions, which could increase fertilization success. These results enhance our ability to predict population extinctions and ecosystem range shifts under projected declines in ocean pH and increases in ocean temperature.

Response of upwelling variability to the local and remote forcing in the Banda Sea

The Banda Sea experiences a strong upwelling between April and November associated with the seasonal strengthening of the trade winds. Data of surface wind, sea surface temperature (SST) and salinity in the period of 1990-2008 were used to further study the response of upwelling to the local and remote forcing in the Banda Sea. A local forcing (Ekman Pumping) during Southeast Monsoon plays role in contributing the upwelling intensity indicated by shallower thermocline and colder SST. In addition, this study exhibits that the upwelling strength is controlled remotely by El Ñino Southern Oscillation (ENSO) where during El Niño (La Niña) periods in Southeast Monsoon, the upwelling weakens (strengthens) in the Banda Sea.

Upper Ocean Response to the Tropical Cyclone Ockhi and its Impact on Primary Production in Arabian Sea

This study investigates the upper ocean response and primary productivity over Arabian Sea due to tropical cyclone ‘Ockhi’, a rare tropical storm system that formed over southwest Bay of Bengal and moved westward into the Arabian Sea while rapidly intensifying into a severe storm. Multi-satellite data products comprising Sea Surface Temperature (SST), turbulent fluxes, surface wind, and Ekman pumping derived from European Reanalysis – 5 (ERA5) daily surface wind data is used to examine the evolution and life cycle of the storm. MODIS derived Chlorophyll-a (Chlor-a), daily averaged Photosynthetically Available Radiation (PAR) and Particulate Organic Carbon (POC) are utilized for detailed analysis of the impact of the storm. Evolution of SST starting from the week prior to Ockhi shows that Southeast Arabian Sea and South-west Bay of Bengal regions had high values ranging from 28 to more than 30ÂoC, temperatures favorable enough to fuel the intensification of Ockhi. As the storm system moved north-westward, a clear reduction in SST is observed over the west-central Arabian Sea, affirming the upper ocean cooling associated with strong upwelling in the storm centre.

Surface chlorophyll-a variations in the Southeastern Tropical Indian Ocean during various types of the positive Indian Ocean Dipole events

ABSTRACT Surface chlorophyll-a (chl-a) variation in the Southeastern Tropical Indian Ocean (SETIO) shows different patterns in response to the various types of the Indian Ocean Dipole (IOD) events. Thirteen years of remotely sensed surface chl-a data from the Moderate-resolution Imaging Spectroradiometer (MODIS) were used to evaluate interannual surface chl-a variation in the SETIO. During the period of analysis (January 2003-December 2015), there were three canonical positive IOD (pIOD) and four pIOD Modoki events. It is found that the spatial patterns of surface chl-a variation were coherent with the pattern of surface wind anomaly, and the sea surface temperature anomaly (SSTA). During canonical pIOD events, high chl-a concentrations were observed in the vicinity of the Sunda Strait and along the coast of western tip of the Java Island around the Cilacap region. Meanwhile, during pIOD Modoki event, surface chl-a concentration was relatively higher and distributed wider than those observed during canonical pIOD event. The analysis shows that relatively weak upwelling event indicated by a deep isothermal layer depth (ILD) during pIOD Modoki events combined with thin barrier layer thickness (BLT) and deep mixed layer provides a favourable condition for an increase in surface chl-a in the SETIO region. Meanwhile, strong upwelling as indicated by shallow ILD combined with thick BLT and shallow mixed layer prevents surface chl-a to increase during canonical pIOD events.