Seasonal Ekman upwelling in the Southwest Sumba from INDESO Model

Southwest Sumba water is part of the Indonesian fisheries management region (WPP573). Marine fisheries resources are influenced by oceanographic phenomena such as an upwelling event. This study aims to describe characteristics of seasonal Ekman upwelling by analyzing oceanographic parameters from the validated INDESO model output (2008-2014). It shows that upwelling event in the study area occurs during the Southeast Monsoon period, which creates an Ekman drift of 0.26 Sv towards offshore. This transported water mass is then replaced by an upwelled vertical flow of sub-surface colder and nutrient-rich water at the velocity of the order of 10−4 m/s. Surface features of the upwelling event are seen from a minimum temperature (24.3 °C), sea level anomaly (0.34 m), but the maximum of chlorophyll-a (3.02 mg/m3). During this time, an uplifted isotherm of 25.5 °C is found from sub-surface to 10 m depth, but it is outcropped at the sea surface in the centre of upwelling area. Interestingly, during upwelling event, salinity stratification revealed an isohaline of 34.10 psu is much deeper at 40 m depth, and much fresher water mass from the Ombai Indonesian Throughflow water is dominant. Averaged temperature-based upwelling index between June-September is about 0.3 °C.

A salty deep ocean as a prerequisite for glacial termination

Deglacial transitions of the middle to late Pleistocene (terminations) are linked to gradual changes in insolation accompanied by abrupt shifts in ocean circulation. However, the reason these deglacial abrupt events are so special compared with their sub-glacial-maximum analogues, in particular with respect to the exaggerated warming observed across Antarctica, remains unclear. Here we show that an increase in the relative importance of salt versus temperature stratification in the glacial deep South Atlantic decreases the potential cooling effect of waters that may be upwelled in response to abrupt perturbations in ocean circulation, as compared with sub-glacial-maximum conditions. Using a comprehensive coupled atmosphere–ocean general circulation model, we then demonstrate that an increase in deep-ocean salinity stratification stabilizes relatively warm waters in the glacial deep ocean, which amplifies the high southern latitude surface ocean temperature response to an abrupt weakening of the Atlantic meridional overturning circulation during deglaciation. The mechanism can produce a doubling in the net rate of warming across Antarctica on a multicentennial timescale when starting from full glacial conditions (as compared with interglacial or subglacial conditions) and therefore helps to explain the large magnitude and rapidity of glacial terminations during the late Quaternary.

Post-Closure Safety Analysis of Nuclear Waste Disposal in Deep Vertical Boreholes

Isolation of spent nuclear fuel assemblies in deep vertical boreholes is analyzed. The main safety features of the borehole concept are related to the repository’s great depth, implying (a) long migration distances and correspondingly long travel times, allowing radionuclides to decay, (b) separation of the repository from the dynamic hydrological cycle near the land surface, (c) stable geological and hydrogeological conditions, and (d) a geochemically reducing environment. An integrated simulation model of the engineered and natural barrier systems has been developed to examine multiple scenarios of the release of radionuclides from the waste canisters, the transport through a fractured porous host rock, and the extraction of potentially contaminated drinking water from an aquifer. These generic simulations include thermal effects from both the natural geothermal gradient and the heat-generating waste, the influence of topography on regional groundwater flow, moderated by salinity stratification at depth, and the role of borehole sealing. The impact of these processes on the transport of select radionuclides is studied, which include long-lived, soluble, sorbing or highly mobile isotopes along with a decay chain of safety-relevant actinide metals. The generic analyses suggest that a deep vertical borehole repository has the potential to be a safe option for the disposal of certain waste streams, with the depth itself and the stable hydrogeological environment encountered in the emplacement zone providing inherent long-term isolation, which allows for reduced reliance on a complex engineered barrier system.

Preliminary Identification to Local Coral Bleaching Event in Manjuto Beach, Pesisir Selatan Regency, West Sumatra: Hydro-Oceanographic Perspectives

Highlight ResarchThe cause of local coral bleaching in Manjuto Beash has been addressed.The influence of ebb-tide cycles on salinity mixing and stratification was analyzed.Spatial analysis Digital Shoreline Analysis System (DSASv5) was conducted to determine the coastline changes in Manjuto Beach.Flow model flexible mesh was simulated to determine the flow pattern within Sungai Pinang Bay.AbstractIn October 2019, the local community reported the occurrence of coral bleaching of a colony of Acropora sp. at Manjuto Beach, Pesisir Selatan Regency experienced bleaching. It was published in several local news, becoming a trending topic among local and central government authorities and coastal communities. There were many inaccuracies about the cause of this phenomenon. This study aimed to identify the causes of local coral bleaching in Manjuto Beach based on oceanographic perspectives. The water quality data collected using TOA DKK water quality checker in the surrounding Manjuto Beach were assessed descriptive-statistically. This study also analyzed the spatial changes of the coastline using DSASv5. A time series of tidal data was also used to analyze the tidal range-induced salinity stratification. A flow model with a flexible mesh was also simulated to determine the water mass movement and longshore current patterns in Manjuto Beach. Dissolved oxygen (DO), temperature, and salinity showed anomalies compared to the water quality standard to support marine life. During both flood and ebb tides, it ranged from 5.8-11.2 mg/L, 28-28.3oC, and 25-28 o/oo, respectively. The other parameters measured (pH, conductivity, turbidity, and density) were suitable for marine biota. The findings show that tidal range has a unique influence on salinity stratification. The intrusion of groundwater supply resulted in lowering of salinity, inducing local coral bleaching in Manjuto Beach. Changes in salinity levels were also triggered by tidal current ranging from 0-0.31 m/s resulting in cumulative salinity shock. Currently, Manjuto Beach is experiencing accretion ranging from 2.36-3.17 m/year, altering the water coverage through the flood-ebb cycles. Those states cause cumulative sun rays’ exposures and salinity shock induced by flood-ebb cycles. That is why local coral bleaching event is undoubtedly avoided.

Temporal and Spatial Variability Scales of Salinity at a Large Microtidal Estuary

The Río de la Plata is a large fluvial–estuarine–sea system discharging into the southwestern Atlantic Ocean, which has relevant features such as high fluvial discharge, microtidal astronomical tidal scales, a relevant meteorological tide, and a strong atmospheric forcing effect, due to its large width. The objective of this study is to advance the understanding of the estuarine hydrodynamics and salt transport, as well as discussing the main characteristics of the spatiotemporal variability of the salinity field. To achieve this, the results of a 3D model of the Río de la Plata and its maritime front were used, simulating an extensive period of 10 years. In this study, the model was validated using vertical salinity profiles collected at different locations in the estuary. The temporal variability of the salinity stratification was characterised at different temporal scales: annual, monthly, and storm. At the same time, the influences of fluvial flow and winds were determined. The correlation analysis between fluvial flow and the salinity field showed that high annual fluvial flows generate an extension of the freshwater area, with larger longitudinal salinity gradients and a shift of the salinity front towards the ocean. The tendency at the monthly scale is not as clear as that observed at the annual scale. The results show that the effect of a storm coming from the northwest is quite similar to that of storms coming from the southwest, especially in the central and southern zones of the Río de la Plata, where mixing increases and stratification decreases, according to the intensity of the storm. The effect of south–southeasterly storms increases the mixing process and reduces stratification; the opposite effect was identified with respect to northeasterly storms, under the influence of which the stratified area increases. Synthesising the obtained results, a global zonification of the vertical salinity stratification for the Río de la Plata is proposed.

Glacial carbon cycle changes by Southern Ocean processes with sedimentary amplification

Recent paleo reconstructions suggest that increased carbon storage in the Southern Ocean during glacial periods contributed to low glacial atmospheric carbon dioxide concentration (pCO2). However, quantifying its contribution in three-dimensional ocean general circulation models (OGCMs) has proven challenging. Here, we show that OGCM simulation with sedimentary process considering enhanced Southern Ocean salinity stratification and iron fertilization from glaciogenic dust during glacial periods improves model-data agreement of glacial deep water with isotopically light carbon, low oxygen, and old radiocarbon ages. The glacial simulation shows a 77-ppm reduction of atmospheric pCO2, which closely matches the paleo record. The Southern Ocean salinity stratification and the iron fertilization from glaciogenic dust amplified the carbonate sedimentary feedback, which caused most of the increased carbon storage in the deep ocean and played an important role in pCO2 reduction. The model-data agreement of Southern Ocean properties is crucial for simulating glacial changes in the ocean carbon cycle.

Viable Putative Vibrio vulnificus and parahaemolyticus in the Pensacola and Perdido Bays: Water Column, Sediments, and Invertebrate Biofilms

Vibriosis is the general term for human illnesses caused by infection of pathogenic Vibrio species. Vibrio vulnificus (Vv) and parahaemolyticus (Vp) are two problematic waterborne pathogens that have yet to be enumerated in northwest Florida coastal Gulf of Mexico estuaries. In this regionally novel study, we surveyed 43 locations in two subtropical estuarine systems, Perdido Bay and Pensacola Bay, over seven dates in winter 2020. Sampling included three substrate types: surface waters, sediments, and invertebrate biofilms. We determined baseline abundances of presumptive viable Vv and Vp appearing as colonies on CHROMagar (Vv, blue; Vp, purple). Vv was detected in 37 out of 43 water samples, with maximum levels of 3,556 CFU/mL. Vp was only detected in 15 water samples, with a maximum concentration of 8,919 CFU/mL. Sediments contained Vv in all but one sample, with concentrations ranging from 121 to 607,222 CFU/mL. In contrast, Vp were only detected in 33 sediment samples, where concentrations ranged from 28 to 77,333 CFU/mL. Opportunistically-sampled surface swabs (biofilms), collected from shells (either oyster or barnacle) and polychaete worms found in sediment samples, contained on average 7,735 and 1,490 CFU/mL of Vv and Vp, respectively. Surface water Vv abundances covaried with bottom water pH, maximum prior cumulative wind speeds, and tidal coefficient on the day of sampling. Vp surface water abundances negatively correlated with surface water salinity, surface water pH, and bottom water pH and positively correlated with total surface dissolved inorganic and total Kjeldahl nitrogen concentrations, and wind. Spatially, there was large variation in Vibrio densities in surface waters; abundances of both species were strongly correlated with wind, suggesting resuspension was important. Sedimentary abundances of both putative Vv and Vp shared a correlation with one parameter: salinity stratification. Due to the length of this study, temperature was not considered a major factor. This short-term (1 month) study was designed not to enumerate pathogenic Vv or Vp, but rather to establish the first winter baseline of Vibrio abundances for this region. Determination of these baseline winter cultivable putative Vibrio abundances will be valuable in predicting relative risk factors in each waterbody of interest.

Sea Surface Salinity Response to Tropical Cyclones Based on Satellite Observations

Multi-year records of satellite remote sensing of sea surface salinity (SSS) provide an opportunity to investigate the climatological characteristics of the SSS response to tropical cyclones (TCs). In this study, the influence of TC winds, rainfall and preexisting ocean stratification on SSS evolution is examined with multiple satellite-based and in-situ data. Global storm-centered composites indicate that TCs act to initially freshen the ocean surface (due to precipitation), and subsequently salinify the surface, largely through vertical ocean processes (mixing and upwelling), although regional hydrography can lead to local departure from this behavior. On average, on the day a TC passes, a strong SSS decrease is observed. The fresh anomaly is subsequently replaced by a net surface salinification, which persists for weeks. This salinification is larger on the right (left)-hand side of the storm motion in the Northern (Southern) Hemisphere, consistent with the location of stronger turbulent mixing. The influence of TC intensity and translation speed on the ocean response is also examined. Despite having greater precipitation, stronger TCs tend to produce longer-lasting, stronger and deeper salinification especially on the right-hand side of the storm motion. Faster moving TCs are found to have slightly weaker freshening with larger area coverage during the passage, but comparable salinification after the passage. The ocean haline response in four basins with different climatological salinity stratification reveals a significant impact of vertical stratification on the salinity response during and after the passage of TCs.