Variability Of Water Masses Research Articles

Water Mass Structure and Variability in the Kane Gap (Equatorial Atlantic Ocean)

Water Mass Structure and Variability in the Kane Gap (Equatorial Atlantic Ocean)

Ocean-atmosphere-ice processes in the Ross Sea: A review

The Ross Sea has been the site of extensive investigations since the earliest days of polar exploration. The International Geophysical Year of 1957-58 enhanced research activities with the establishment of scientific stations and the collection of oceanographic observations in the area. While many features of its oceanography, ecology, physics, glaciology, geology, and biogeochemistry are known, recent advances provide new insights into its structure and function, as well as into its relationship to global climate. We present a comprehensive review of the advances of understanding the main processes occurring in the area, such as the formation of dense shelf water and the production of Antarctic Bottom Water (AABW), as well as the main drivers (at both large and local scales) of local dynamics and water mass variability. We also summarize the main modeling applications, which are still limited and need to be improved using high-resolution models and, locally, limited-area models to explain processes driven mainly by thermodynamics and water-mass transformations. The Ross Sea forms the most saline AABW due to the activity of two polynyas in the western sector. A salinity gradient occurs on the shelf, with fresh Low Salinity Shelf Waters concentrated in the eastern Ross Sea, which is influenced by the inflow of fresh water from the Amundsen and Bellingshausen Seas. This freshwater inflow was thought to be the cause of a multi-decadal freshening of the High Salinity Shelf Water, precursor to the AABW, although a rebound in salinity in the Ross Sea has been observed since 2014. The increase in salinity has also affected the production of AABW, with the respective rebound occurring almost simultaneously.

Winter distribution of zooplankton and ichthyoplankton assemblages in the North Sea and the English Channel.

Although zooplankton were extensively studied in the North Sea, knowledge about winter zooplankton assemblages is still scarce, despite potential influence of zooplankton overwintering stocks on seasonal plankton succession and productivity. Furthermore, several economically and ecologically important fish species reproduce during winter contributing to the zooplankton community as passive members (eggs) or predators (larvae). To elucidate on winter zooplankton distribution, abundance and composition in the Southern North Sea and Eastern English Channel, we defined assemblages based on mesozoo- and ichthyoplankton data sampled between January and February 2008 using fuzzy-clustering and indicator species. Mesozoo- and ichthyoplankton (eggs+larvae) were integrated in a common analysis by using a spatial grid adapted to the datasets and defined by means of a geostatistical method developed in agronomics. Potential environmental drivers of assemblage distribution were evaluated by means of GLMM and comparison with data from 2022 facilitated insight about the inter-annual representativeness of the assemblages. Five zooplankton assemblages were found varying with regard to total zooplankton abundance, dominant and indicator taxa. Spatial variability of abiotic (dissolved nutrients, salinity, depth, temperature, organic matter in suspension, chlorophyll a), biotic variables (phyto- and microplankton composition), water masses and fish spawning grounds were revealed as potential drivers of assemblage distribution. Assemblages off the Rhine-Scheldt estuary and in the German Bight harbored the biggest zooplankton overwintering stocks that might influence the grazing pressure on phytoplankton spring production. Assemblages off the Rhine-Scheldt estuary and covering the English Channel and the Southern Bight were found to be of high importance for herring and plaice larvae. Although further analyses suggested inter-annual representativeness of the assemblages found (2008 vs 2022), the assessment of further years would be necessary to account for potential inter-annual variability. Future studies could profit from the assessment of microzooplankton facilitating insight in fish larvae feeding potential and zooplankton overwintering strategies.

Bi-layered spring-neap variability of water masses in estuaries and the impact of human activities

Estuaries are one of the most important ecosystems in the world, which are economically developed and densely populated. However, the intricate hydrodynamic environment and frequent human activities within estuaries have left the spatiotemporal variability of water properties in these areas inadequately understood. Recently, based on in situ observations and numerical simulations, we found significant spring-neap variability of water mass properties in the Yangtze River Estuary, which exhibited a bi-layered vertical structure. In the Yangtze River Estuary, salinity could decrease (increase) over 4 psu during spring (neap) tides in the upper layer, and satellite observations confirmed that both sea surface chlorophyll-a concentration and particulate organic carbon concentration also showed significant spring-neap variabilities. Decreasing salinity in the upper layer induced a shoreward pressure gradient force in the lower layer, which caused shoreward advection of high salinity water from the deep ocean and resulted in salinity increasing up to 2 psu in the lower layer of the Yangtze River Estuary. Dynamical diagnoses proved that spring-neap variability of water mass properties were caused by the asymmetry of tidal currents via modulating the ratio of freshwater to seawater. Similar situations also occurred in the Mississippi River Estuary. Furthermore, constructions of dams and other hydraulic projects in the watershed could greatly alter the locations with significant spring-neap water masses variability through reducing the riverine sediment flux and thus, leading to the erosion of the tidal flats in estuaries. The above results highlight the important roles of tidal asymmetry and human activities in affecting spring-neap variabilities of water mass properties in estuaries.

Short-term time-series observations of phytoplankton light-absorption and productivity in Prydz Bay, coastal Antarctica

The optical characteristics of coastal Antarctic waters exhibit complexity due to the dynamic hydrography influenced by meltwater intrusion, which alters nutrient levels, thermohaline structure, and optically active substances (OAS) regimes. Studies on bio-optical variability and its implications on phytoplankton productivity (PP) are scanty in coastal polar regions. On this backdrop, time-series measurements (72 h at 6 h intervals) of bio-optical properties such as phytoplankton biomass (chlorophyll-a), absorption (aph), and total suspended matter (TSM) concurrently with PP were measured to understand their interplay and variability in relation to the ambient physicochemical settings in the under-sampled Prydz Bay, coastal Antarctica. Our findings revealed thermohaline stratification within the bay, likely attributed to the inflow of less saline meltwater from nearby glaciers and minimal wind activity. The consistent presence of sub-surface chlorophyll maximum (SCM) beneath the stratified layer underscored the light-acclimatization response of shade-adapted phytoplankton. Surface waters exhibited higher TSM compared to deeper layers, indicating glacial melt influence, while the depth of the sunlit layer remained relatively stable, suggesting limited water mass movement and/or variability in OAS at the study site. An inverse relation between chlorophyll-a and chlorophyll-a-specific phytoplankton light absorption (a*ph(λ)) manifested ‘pigment package effect’ within the prevailing phytoplankton community, implying reduced light-absorption efficiency and consequent lower PP. Compared to chlorophyll-a, the phytoplankton light absorption (aph(λ)) emerged as a better proxy for explaining PP variability. Nutrient availability was not limiting, which was conducive to micro (large) phytoplankton growth. Classification of phytoplankton size classes (micro, nano, and pico) based on the B/R ratio (aph at Blue (443 nm)/Red (676 nm) region) confirmed the dominance of larger (micro) phytoplankton that are more susceptible to package effect, thus have implications on reduced PP potential of this polar marine ecosystem.

VARIABILITY OF EQUIVALENT WATER HEIGHT (EWH) IN INDONESIA DURING 14 YEARS OF GRACE GRAVITY SATELLITE MISSION

GRACE Satellite (Gravity Recovery and Climate Experiment) is a gravity monitoring satellite, that is very sensitive to mass changes, especially the signals that produce by redistribution of water masses. Data from this satellite can be used to observe water distribution in the form of spherical harmonic coefficients. Water mass variations are presented as Equivalent Water Height (EWH). The results of GRACE processing showed that the largest EWH was 27.298 cm in January 2015 and the smallest EWH was 29.816 cm in June 2004 in Sumatera Island. The positive trend occurred in Sumatra island and the negative trend occurred in eastern Indonesia. Generally, the trend of Indonesian rainfall throughout 2002 to 2016 was constant. However, there was a change in seasonal patterns in 2014. This research also use Mascon data from GRACE satellite to determine the radius of the gaussian filter and TRMM satellite’s data to observe rainfall data to be compared with the EWH variability from GRACE.

Monitoring the response of Saudi Arabia's largest fossil aquifer system to climate variability

The study utilizes an integrated approach that involves GRACE and Global Precipitation Climatology Project (GPCP) data to analyze temporal water mass variations in Saudi Arabia (KSA). Recently, KSA has witnessed a historic wet period between 2018 and 2020 (i.e., 120–150 mm/year) following a prolonged dry period between 2002 and 2017 (i.e., 80–100 mm/year). Inspection of GRACE data showed a decline in groundwater recharge of −4 to −6 mm during the dry period. The depletion was reduced by 1 to 6.8 mm in the Northeastern side of KSA (e.g. Hail, Al-Jouf, Al-Hudud Ash-Shamaliyah areas) during the wet period. This impressive recovery has led to a groundwater recharge increase of 360 km3 in Hail, 174 km3 in Al-Jouf and 97 km3 in Al-Hudud Ash-Shamaliyah. The findings emphasize the notion that climate change will bring more frequent extreme climatic events to the Kingdom of Saudi Arabia and call for continuous monitoring of aquifers every year.

Water masses influence the variation of microbial communities in the Yangtze River Estuary and its adjacent waters.

The Yangtze River estuary (YRE) are strongly influenced by the Kuroshio and terrigenous input from rivers, leading to the formation of distinct water masses, however, there remains a limited understanding of the full extent of this influence. Here the variation of water masses and bacterial communities of 58 seawater samples from the YRE and its adjacent waters were investigated. Our findings suggested that there were 5 water masses in the studied area: Black stream (BS), coastal water in the East China Sea (CW), nearshore mixed water (NM), mixed water in the middle and deep layers of the East China Sea (MM), and deep water blocks in the middle of the East China Sea (DM). The CW mass harbors the highest alpha diversity across all layers, whereas the NM mass exhibits higher diversity in the surface layer but lower in the middle layers. Proteobacteria was the most abundant taxa in all water masses, apart from that, in the surface layer masses, Cyanobacterium, Bacteroidota, and Actinobacteriota were the highest proportion in CW, while Bacteroidota and Actinobacteriota were the highest proportion in NM and BS; in the middle layer, Bacteroidota and Actinobacteriota were dominant phylum in CW and BS masses, but Cyanobacterium was main phylum in NM mass; in the bottom layer, Bacteroidota and Actinobacteriota were the dominant phylum in CW, while Marininimicrobia was the dominated phylum in DM and MM masses. Network analysis suggests water masses have obvious influence on community topological characteristics, moreover, community assembly across masses also differ greatly. Taken together, these results emphasized the significant impact of water masses on the bacterial composition, topological characteristics and assembly process, which may provide a theoretical foundation for predicting alterations in microbial communities within estuarine ecosystems under the influence of water masses.

Efficiency Improvement, Design Optimization, and Expansion of Oxygen Flow Valve Holes in Small Industrial Scale Husk Furnaces

Indonesia has an abundant amount of industry. Production in large, medium, and small industries still uses gas and oil as fuel sources. The fuel sources used still come from non-renewable energy. There is a need for alternative use of renewable energy to reduce the use of non-renewable energy. One solution is the use of rice husk biomass as a fuel source. Rice husk is still often considered as waste despite its many utilizations. The utilization of rice husk waste must be improved to increase its beneficial value. Rice husk waste can be utilized as a fuel source in a husk furnace. A husk furnace is a cooking device in which the fuel (rice husk) is burned using direct combustion. This research aims to optimize the efficiency of the husk furnace by varying the size of the oxygen flow valve hole and the mass of water being heated. Tests were conducted on four variations of oxygen flow valve hole size, namely, 36x27 cm2, 36x34 cm2, 43x34 cm2, and 50x34 cm2, and two variations of water mass (6 and 18 kg). The research was conducted by heating water using the Water Boiling Test method with test parameters: heating time, fuel consumption rate, energy in, energy out, heat efficiency, heat transfer rate, and ash and charcoal yield. The significant efficiency value can be used as a reference for small-scale industrial rice husk furnaces. The most significant efficiency in the study was 54.99%, achieved by a 43x34 cm2 valve hole for heating 18 kg of water. Based on the most effective efficiency value gained, the expansion of the oxygen flow valve hole is sufficient to be used as a test parameter to test the optimization of small industrial-scale husk furnaces.

Global biogeography of the smallest plankton across ocean depths.

Tiny ocean plankton (picoplankton) are fundamental for the functioning of the biosphere, but the ecological mechanisms shaping their biogeography were partially understood. Comprehending whether these microorganisms are structured by niche versus neutral processes is relevant in the context of global change. We investigate the ecological processes (selection, dispersal, and drift) structuring global-ocean picoplanktonic communities inhabiting the epipelagic (0 to 200 meters), mesopelagic (200 to 1000 meters), and bathypelagic (1000 to 4000 meters) zones. We found that selection decreased, while dispersal limitation increased with depth, possibly due to differences in habitat heterogeneity and dispersal barriers such as water masses and bottom topography. Picoplankton β-diversity positively correlated with environmental heterogeneity and water mass variability, but this relationship tended to be weaker for eukaryotes than for prokaryotes. Community patterns were more pronounced in the Mediterranean Sea, probably because of its cross-basin environmental heterogeneity and deep-water isolation. We conclude that different combinations of ecological mechanisms shape the biogeography of the ocean microbiome across depths.

Deep-sea response to interglacial-glacial variability on the South Australian margin over the last 94 ka

The continuous record offered by deep-sea sediments has been extensively used to constrain shifting continental and oceanographic conditions. Yet, past fluctuations in deep-sea benthic conditions and bottom-currents are in numerous parts of the globe scarcely documented, one such example being the South Australian margin. Indeed, though variations in surface water masses and continental aeolian dust and river outflow are well documented in the area, little is known about benthic environments and their dynamics during the last interglacial-glacial cycle. We focus here on benthic foraminiferal assemblages sampled from a sediment core recovered at 2420 m depth from a small plateau south of Kangaroo Island within the underwater Murray Canyons Group (South Australian margin). Benthic foraminiferal assemblages show a distinct separation between interglacial and glacial periods over the last 94 ka, and indicate that the benthic environment was well-ventilated and oligotrophic during glacial periods, whilst being rather marked by reduced oxygenation associated to higher food input during the Holocene and Marine Isotope Stage 5a-c. We demonstrate that autochtonous deep-sea benthic foraminiferal communities neither respond to changes in the Murray River's discharges, nor do they follow variations in aeolian dust input from South Australia. Instead, the deep-sea and the terrestrial realm appear decoupled. Moreover, our observations suggest that bottom-water slope currents were stronger during the Holocene and Marine Isotope Stage 5a-c. We propose that this strengthening was triggered by an intensification of the poleward-circulating deep eastern boundary current transporting carbon-rich Indian Deep Water. In contrast, glacial seafloor conditions, especially during the Last Glacial Maximum, may reflect a greater influence and a shoaling of oxygen-rich Antarctic Bottom Water of South Australia. This bottom-water shift would follow the northward displacement of the Subtropical and Subantarctic Fronts and coincide with a withering influence of the Leeuwin Current within surface waters.

The role of wind and buoyancy forcing on mixed layer depths and productivity on the Chatham Rise from ocean glider and ship-based observations

ABSTRACT The Subtropical Front (STF) and associated biological productivity are topographically locked to the Chatham Rise. Year-to-year differences of upper ocean dynamics and associated responses of phytoplankton are valuable for understanding variability in fisheries biomass as well as providing new knowledge of environmental condition for potential seabed mining in this keystone ecosystem. In-situ observations collected over three consecutive years are used to examine the oceanographic variability on Chatham Rise and its potential causal mechanisms are evaluated from satellite observations and a global atmospheric reanalysis. The water column over Chatham Rise consists of a three-layer structure comprised of a stable intermediate layer sandwiched between a well-mixed surface and bottom layer. The in-situ data showed that different water masses can dominate the surface mixed layer at different times. This variability in surface water masses appears to be related to the position of the STF modulated by wind forcing. Spatial and temporal variability was also observed in the mixed layer depth with the temporal variability driven mainly by wind forcing. A strong relationship was observed between phytoplankton biomass and the depth of the mixed layer with implications for the distribution of biological communities and fisheries at the year-to-year timescale on the Chatham Rise.

Micropaleontological and Isotopic Perspective of Surface Water Mass Variability in the NE Atlantic from MIS 6 to 5e (188 to 115 ka)

The penultimate glaciation (marine isotope stage (MIS) 6) is considered regionally extreme compared to the last glacial maximum, in which the European ice sheets had a vast areal extent. In contrast to the last deglaciation (19–7 ka), the penultimate deglaciation (140–130 ka) hosts one of the most rapid oceanographic changes of the late Pleistocene. In this study, we reconstructed changes in the near-surface and thermocline in the central to northeast Atlantic by analyzing sediments from two Integrated Ocean Drilling Program Expedition 306 sites. Sites U1313 (41°00.6′ N, 32°57.4′ W) and U1314 (56°21.9′ N, 27°53.3′ W) were drilled on the eastern flank of the mid-Atlantic ridge and Gardar Drift of the eastern subpolar North Atlantic, respectively. We analyzed planktonic foraminiferal assemblages, ice-rafted debris (IRD), and oxygen isotopes in two planktonic foraminifers, Globigerina bulloides, and Globorotalia inflata, from MIS 6 to 5e (185–115 ka). Warmer and colder sea-surface conditions were marked by a change in the relative abundance of polar, subpolar, and transitional planktonic foraminifers. Oxygen isotopes in G. bulloides and G. inflata suggest that the thermocline deepened at the subtropical Site U1313 during MIS 6. The lack of Globorotalia inflata prevented us from profiling the mixed layer and thermocline at the subpolar Site U1314. In contrast to MIS 6, the mixed layer and thermocline were re-stratified during the last interglacial. The lack of major IRD events at both sites suggests the stability of the Laurentide ice sheet during MIS 6 compared to the subsequent glaciation. The presence of Heinrich event 11 indicates the discharge of freshwater that freshened the sea surface, resulting in mixing between the mixed layer and thermocline. Our results were placed into a broader context using published data that shed light on the sensitivity of freshwater discharge to the North Atlantic and the following changes with a transition from a penultimate glacial to an interglacial period in surface circulation.

Water Mass Variations in the Maluku Channel of the Indonesian Seas During the Winter of 2018–2019

AbstractAn autonomous underwater glider was deployed in the Maluku Channel during 1 December 2018 through 21 February 2019 to measure temperature and salinity profiles of the upper ∼1,000 m continuously. The measurements suggest intraseasonal variations of the Pacific water mass intrusions into the Maluku Channel, which has not been reported before. The North Pacific Tropical and Intermediate Waters are found to intrude episodically into the eastern Maluku Channel at the depths of 130–180 m and 250–300 m, respectively, during January through February of 2019, each lasting for a few days to a week. The Antarctic Intermediate Water was present in the middle and western Maluku Channel between 600 and 800 m with intraseasonal variability. The South Pacific Subsurface Water was only found to intrude into the eastern Maluku Channel between 250 and 300 m during the first two transections in early December of 2018. Concurrent meter data from three moorings in the Maluku and Talaud‐Halmahera Channels are used to verify the water mass movement. The subsurface and intermediate water mass variations here are found to be closely related to the swing of the Mindanao Current near the Maluku Channel. These intraseasonal water mass intrusions are important aspects of water exchange between the western Pacific Ocean and the Indonesian seas.

Analysis of the Distribution and Seasonal Variability of the South China Sea Water Masses Based on the K-means Cluster Method

Influenced by local mixing and coastal runoff, water masses in the South China Sea degenerate significantly. The K-means algorithm is used to classify the water masses based on WOD13 temperature and salinity observations from 1966 to 2013 because its principle is consistent with the definition of a shallow water mass. The numbers and initial centers of the water masses are determined using functions of in-cluster distance and density values. The result shows that there are ten water masses in the South China Sea. In combination with the T-S scatter diagram, the properties of the South China Sea water masses were analyzed, including their distribution, the seasonal variability, and the degeneration processes. The temperatures of water masses were higher in summer and lower in winter, with the amplitudes of variation gradually reduced from the surface to the bottom. The seasonal variation in salinity of the surface water masses was high in winter and low in summer, which mainly depends on the amount of river discharge and precipitation. The subsurface water masses were strongly affected by water from the Pacific Ocean; thus, the seasonal variability of these water masses is weak, especially for the intermediate water mass that characterized by prominent low salinity. The water mass formed by the Kuroshio water invading the South China Sea has insignificant seasonal variations in temperature and salinity. The properties and seasonal variabilities of the water masses derived from the K-means algorithm are in agreement with the existing conclusions, suggesting that the improved K-means algorithm is efficient and accurate in the shallow water mass division.

Full-depth vertical distribution of planktonic ciliates (Ciliophora) and a novel bio-index for indicating habitat suitability of tintinnid in the Arctic Ocean

Despite the planktonic ciliate importance in the microzooplankton compartment, their full-depth vertical distribution in the Arctic Ocean was poorly documented as well as the related variations in different water masses. The full-depth community structure of planktonic ciliates was investigated in the Arctic Ocean during summer 2021. The ciliate abundance and biomass decreased rapidly from 200 m to bottom. Five water masses were identified throughout the water column and each one exhibited a unique ciliate community structure. Aloricate ciliates were singled out as the dominant group with average abundance proportion to total ciliates at each depth >95%. Large (>30 μm) and small (10–20 μm) size-fractions of aloricate ciliates were abundant in shallow and deep waters, respectively, which revealed an anti-phase relationship in vertical distribution. Three new record tintinnid species were found during this survey. Pacific-origin species Salpingella sp.1 and Arctic endemic species Ptychocylis urnula occupied the top abundance proportion in the Pacific Summer Water (44.7%) and three water masses (≥38.7%, Mixed Layer Water, Remnant Winter Water, Atlantic-origin Water), respectively. The habitat suitability of tintinnid abundant species was characterised by the Bio-index revealing a distinct death-zone for each species. Variations in survival habitat of abundant tintinnids can be regarded as indicators for the future Arctic climate change. These results provide fundamental data on the microzooplankton response to the intrusion of Pacific waters into the Arctic Ocean upon its rapid warming.

After Two Decades, Argo at PMEL, Looks to the Future

The NOAA Pacific Environmental Laboratory (PMEL) has contributed to the revolutionary Argo ocean observing system since its inception, developing CTD calibration algorithms and software that have been adopted by the international Argo community. PMEL has provided over 1,440 Argo floats—~13% of the global array—with ~500 currently active. PMEL scientific contributions using Argo data have ranged from regional to global analyses of ocean circulation and water-mass variability, to ocean warming and its contributions to sea level rise and Earth’s energy imbalance, to estimates of global ocean deoxygenation. In recent years, PMEL has initiated both Deep Argo (with a regional pilot array of full-ocean-depth profiling floats in the rapidly changing and dynamic western South Atlantic) and Biogeochemical (BGC) Argo (with a pilot array in the biogeochemically diverse and economically important California Current Large Marine Ecosystem). PMEL is also developing innovative near-global maps of ocean physical and biogeochemical parameters using machine learning algorithms that enable investigations of societally important oceanographic phenomena, and an Adopt-A-Float program. Future challenges include growing the financial, infrastructure, and human resources necessary to take the Deep and BGC Argo missions global and to fulfill the One Argo mission of a global, full-depth, multidisciplinary ocean observing array.

Variation of upper-layer flow structures and water masses observed around the Noto Peninsula and Sado Island, Japan

After classifying various water masses around the Noto Peninsula and Sado Island, Japan and identifying their seasonal variation, we investigated flow fields in the area. Distributions of flow structures and water properties were analyzed based on intensive observations using a conductivity–temperature–depth profiler during 2002–2020. Tide gauge and satellite altimetry data were also analyzed to elucidate the temporal and the more widespread horizontal variation of the sea surface geostrophic flow field. Interannual change of the northeastward baroclinic jet formed offshore of the Noto Peninsula in fall was found. Furthermore, anticyclonic eddy formation around Toyama Bay which is part of the current path transition of the coastal branch of the Tsushima Warm Current was found to result from effects of bathymetric change behind the Noto Peninsula. At that time, the sea-surface current speed of the coastal branch was also high. We propose new methods for predicting current path transition events two weeks in advance.

Spatio-temporal variability of terrestrial water storage in the Yangtze River Basin: Response to climate changes

The Yangtze River Basin (YRB) is an important region for China's economic development. However, it has a complex terrain layout, most of which is affected by monsoon weather, and the geographical and temporal distribution of water resources is severely unbalanced. Therefore, the detailed analysis of spatio-temporal water mass changes is helpful to the development and rational utilization of water resources in the YRB. In this study, the variation of terrestrial water storage (TWS) is monitored by Gravity Recovery and Climate Experiment (GRACE) satellite gravity. We find that the University of Texas Center for Space Research (CSR) solution shows a notable difference with the Jet Propulsion Laboratory (JPL) in space, but the general trend is consistent in time series. Then the GRACE inferred water mass variation reveals that the YRB has experienced several drought and flood events over the past two decades. Global Land Data Assimilation System (GLDAS) results are similar to GRACE. Furthermore, the overall precipitation trend tends to be stable in space, but it is greatly influenced by the strong El Niño-Southern Oscillation (ENSO), which is the response to global climate change. The upper YRB is less affected by ENSO and shows a more stable water storage signal with respect to the lower YRB.

Mass Variations in Terrestrial Water Storage over the Nile River Basin and Mega Aquifer System as Deduced from GRACE-FO Level-2 Products and Precipitation Patterns from GPCP Data

Changes in the terrestrial total water storage (TWS) have been estimated at both global and river basin scales from the Gravity Recovery and Climate Experiment (GRACE) mission and are still being detected from its GRACE Follow-On (GRACE-FO) mission. In this contribution, the sixth release of GRACE-FO (RL06) level-2 products applying DDK5 (decorrelation filter) were used to detect water mass variations for the Nile River Basin (NRB) in Africa and the Mega Aquifer System (MAS) in Asia. The following approach was implemented to detect the mass variation over the NRB and MAS: (1) TWS mass (June 2018–June 2021) was estimated by converting the spherical harmonic coefficients from the decorrelation filter DDK 5 of the GRACE-FO Level-2 RL06 products into equivalent water heights, where the TWS had been re-produced after removing the mean temporal signal (2) Precipitation data from Global Precipitation Climatology Project was used to investigate the pattern of change over the study area. Our findings include: (1) during the GRACE-FO period, the mass variations extracted from the RL06-DDK5 solutions from the three official centers—CSR, JPL, and GFZ—were found to be consistent with each other, (2) The NRB showed substantial temporal TWS variations, given a basin average of about 6 cm in 2019 and about 12 cm in 2020 between September and November and a lower basin average of about −9 cm in 2019 and −6 cm in 2020 in the wet seasons between March and May, while mass variations for the MAS had a relatively weaker temporal TWS magnitude, (3) the observed seasonal signal over the NRB was attributed to the high intensity of the precipitation events over the NRB (AAP: 1000–1800 mm yr−1), whereas the lack of the seasonal TWS signal over the MAS was due to the low intensity of the precipitation events over the MAS (AAP: 180–500 mm yr−1).