Ocean Dynamics最新文献

Abstract

The Odra estuary in the southern Baltic Sea comprises the Odra (Szczecin) Lagoon, the Pomeranian Bay and a number of other shallow water areas and channels. Known for its abundance of fish, eutrophication in the Odra Lagoon is a pressing issue for science and environmental management representing a global problem: What determines the seasonal variability of nitrogen and nitrogen turnover in shallow water areas, and how does seasonal variability change due to climatic changes such as warming and sea level rise? How do such changes affect nutrient exports to the regional ocean? This study employs a high-resolution unstructured model system to investigate physical-biogeochemical interactions, nitrogen turnover, and conditions leading to nitrogen export to the Baltic Sea within the Odra estuary. The research comprises hindcast and a climatic experiment with modified water level and temperature inputs. The model reproduces the thermohaline dynamics of brackish shallow water areas, phytoplankton blooms and the variability of inorganic nitrogen. The simulations identify the dynamic partitioning of the Odra Lagoon into the highly eutrophic, lake-like Small Lagoon and more frequently flushed, zooplankton-rich Great Lagoon. Although the two years of the hindcast simulation feature very different boundary conditions in terms of river forcing, comparable patterns of seasonal nitrogen export emerge. In a climate change experiment with increased sea levels and global temperatures, the system appears sensitive, but remains stable with regard to nutrient transport and is therefore predictable. The climate change experiment reveals enhanced primary producer biomass concentrations, suggesting heightened eutrophication. While in the shallow waters of Odra Lagoon oxygen concentration remains relatively stable, oxygen depletion intensifies as the lagoon outflows enter the Pomeranian Bay. This phenomenon is linked to increased denitrification within the stratified Odra plume. Deeper, meandering channels, such as Swina, demonstrate resilience to oxygen reduction, influenced by sea level rise and enhanced currents. Based on the temporal-spatial high-resolution coupled, validated simulations, it is possible to develop tailor-made management solutions without having to run expensive and complicated observation campaigns in the shallow waters with complex topography.

The Amazon Continental Shelf (ACS) is a shallow region (< 100 m), with a maximum width of 330 km, which encloses the northern portion of the Brazilian continental shelf and has great ecological and climatic importance on a global scale. Although important scientific efforts have been made to understand the hydrodynamics of the ACS and the dispersion of the Amazon River plume, there are still few studies that address surface oceanic water intrusion into the ACS. This study describes the existence of preferential surface oceanic water intrusion pathways into the ACS along 3 sectors: Maranhão (MA shelf), Pará (PA shelf) and Amapá (AP shelf). The analysis is based on: (i) 306 surface drifter trajectories along 1344 km of the ACS (provided by the Global Drifter Program) and (ii) 20 years of Lagrangian simulations (with Parcels model forced by currents from the reanalysis GLORYS). The results show that the MA shelf sector is the main pathway for surface oceanic water intrusions into the ACS, corresponding to 56% of the intrusions, followed by PA shelf (43%) and AP shelf (1%). During the austral summer, intrusions occur with a higher frequency in PA and AP shelf. The MA shelf shows weak seasonality in the intrusions. The temporal variability of particle intrusion rates into the ACS is directly related to the variability of the trade winds, and the meso-scale circulation associated with the North Brazil Current and the North Equatorial Countercurrent.

The bidirectional mass exchange between the Marmara Sea and the Aegean Sea provides one part of the critical hydrodynamic links between the Black Sea and the Mediterranean Sea. In this study, we examined exchange in the Dardanelles based on a 3-D numerical model simulation covering an 11-year period under realistic atmospheric forcing. The model includes the Black Sea, the Marmara Sea, and a part of the Aegean Sea to include the remote effects of basin dynamics. The main features as one-, two-, and three-layered flow structures are successfully reproduced by the model in comparison to earlier observations. It is found that the strait is subject to submaximal exchange by only one control near the Nara Pass. According to long-term modeling results, most variability occurs on synoptic time scales, and wind stress has a dominant role in those variations. The seasonal and interannual variability of exchange flow is relatively low and displays a close relationship with freshwater input to the Black Sea.

Recent studies found that on long time scales there are often unexplained opposite trends in sea level variability between the upper and lower Chesapeake Bay (CB). Therefore, daily sea level and temperature records were analyzed in two locations, Norfolk in the southern CB and Baltimore in the northern CB; surface currents from Coastal Ocean Dynamics Application Radar (CODAR) near the mouth of CB were also analyzed to examine connections between the CB and the Atlantic Ocean. The observations in the bay were compared with daily Atlantic Meridional Overturning Circulation (AMOC) observations during 2005–2021. Empirical Mode Decomposition (EMD) analysis was used to show that variations of sea level and temperature in the upper and lower CB are positively correlated with each other for short time scales of months to few years, but anticorrelated on low frequency modes representing decadal variability and long-term nonlinear trends. The long-term CB modes seem to be linked with AMOC variability through variations in the Gulf Stream and the wind-driven Ekman transports over the North Atlantic Ocean. AMOC variability correlates more strongly with variability in the southern CB near the mouth of the bay, where surface currents indicate potential links with AMOC variability. For example, when AMOC and the Gulf Stream were especially weak during 2009–2010, sea level in the southern bay was abnormally high, temperatures were colder than normal and outflow through the mouth of CB was especially high. Sea level in the upper bay responded to this change only 1–2 years later, which partly explains phase differences within the bay. A persistent trend of 0.22 cm/s per year of increased outflow from the CB, may be a sign of a climate-related trend associated with combination of weakening AMOC and increased precipitation and river discharge into the CB.

Motivated by the extreme hydrological events that caused an abnormal reduction and increase in discharge from the Amazon River in 2010 and 2012, respectively, this work investigates the seasonal variability of the sea surface salinity (SSS) in the western tropical Atlantic Ocean over these years. SMOS satellite data and a 1/12(^{circ }) horizontal resolution of the coordinate ocean model (HYCOM) are used to investigate the SSS seasonal variation and assess the balance of mixed layer salinity (MLS) and the mechanisms that rule the SSS seasonal cycle. Two simulations with the same configuration, but with and without tides effects, are employed to investigate the impact of tides on the MLS balance in the region. The results show that the SSS of the Amazon River plume (ARP) was about 1.0 larger and covered a smaller area during the summer and early year boreal autumn of 2012 compared to 2010 in the area located to northwest of the North Brazil Current (NBC) retroflection region, even with the expressive increase in the supply of fresh water from the Amazon River in 2012 compared to 2010. This variability in SSS occurs shortly after the maximum discharge of the Amazon River and is associated with the highest input of freshwater precipitation from the Intertropical Convergence Zone (ITCZ) during the 2010 boreal spring and summer. The impact of tidal swings on the MLS balance in the western region of the tropical Atlantic Ocean occurs mainly in the area near the mouth of the Amazon and Pará Rivers, especially in the northwest portion of the mouth of the Amazon River until approximately Cabo Cassiporé. The forced tidal model shows an increase in MLS over the entire seasonal cycle of about 1.2, as well as a decrease in the contribution of zonal advection to the MLS balance, which reduces the zonal component from the west and increases the meridional component towards the north.

On 22 October 2021, 109 shipping containers fell overboard from the M/V Zim Kingston in rough seas off the coast of Vancouver Island, British Columbia, Canada. While afloat, these shipping containers pose a significant risk to marine traffic in addition to being a source of marine pollution. Out of the 109 shipping containers, 4 were discovered on the beaches of northwest Vancouver Island 5 days later. Drift simulations were made using the standard leeway tables for shipping containers that vary with the immersion fraction of the shipping container. These leeway values over the expected range of immersion levels underestimated the travelled distance of the shipping containers relative to the observed grounding locations. An increase in the leeway of 1.5% of the wind speed improves the agreement between the simulations and observations, which is consistent with the addition of the Stokes drift to the leeway of the shipping container. It is argued that the leeway measured using the direct method, which was used to calculate the leeway of shipping containers, does not implicitly include the Stokes drift as previously suggested. This result suggests that the Stokes drift should be added to the leeway calculated with the direct method. While the error is small over timescales of 24 to 48 h, it accumulates in time and is appreciable for drift prediction greater than 48 h.

Abstract

This study presents the initial findings from analyzing the ocean surface current observations during 2018 from the recently installed high-frequency (HF) radars in the Gulf of Khambhat in the northeastern Arabian Sea, India. The research is structured into two main sections: firstly, the extraction of the major (M2, S2, N2, K1, and O1) and shallow-water (M4, MS4, M6, and M8) tidal currents in the gulf, and secondly, understanding the impact of seasonal riverine freshwater influxes on the M2 tidal currents. The HF radars accurately captured strongest currents of ~2.0 m/s within the gulf. Additionally, the circulation pattern in the western gulf is mostly characterized by zonal currents, in contrast to the eastern gulf, where meridional currents prevail. Based on the findings of the higher harmonic analysis, it is apparent that the M2 tidal currents exhibit the highest magnitude, followed by other semi-daily constituents such as S2 and N2, as well as diurnal tidal constituents including K1 and O1. The M4 tidal currents, which are one of the shallow-water tidal components, exhibit strengths that span from 3.15 to 16.50 cm/s. The enhancement of tidal currents in the nearshore areas (within approximately 50 m) can be attributed to their interaction with the bottom bathymetry and the general coastline geometry of the gulf. Notably, higher values of Richardson number ( ({R}_{i}) ) and Brunt-Väisälä frequency ( ({N}^{2}) ) indicated the presence of highly stratified upper layers, particularly during September. The signatures of higher stratification during September contribute to the highest amplitude (>1.50 m/s) of M2 tidal currents.

Based on a submesoscale-resolving glider observation from April 25 to May 4, 2018, characteristics and underlying dynamics of submesoscale variability at the edge of an anticyclonic eddy shed from Kuroshio in the Northern South China Sea are explored in this study. Three underwater gliders traveled across the frontal zone and implemented ~ 300 dives, covering a horizontal distance of ~ 160 km and a vertical depth of ~ 500 m in 9 days. The character of k⁻² slope for spectral potential energy and the strong lateral buoyancy gradient indicate frontogenesis-induced submesoscale motions on the eddy edge. Further analysis focusing on the potential vorticity and balanced Richardson number reveals the development of symmetric instability (SI), which is associated with the strong lateral gradient of buoyancy at the edge of the anticyclonic eddy in the late spring.

Multi-mission satellite altimetry data have been used to study the spatial and temporal variability in global storm surge water levels. This was done by means of a time-dependent extreme value analysis applied to the monthly maximum detided water levels. To account for the limited temporal resolution of the satellite data, the data were first stacked on a (varvec{5}^{varvec{circ }} times varvec{5}^{varvec{circ }}) grid. Moreover, additional scaling was applied to the extreme value analysis for which the scaling factors were determined by means of a resampling method using reanalysis data. In addition to the conventional analysis using data from tide gauges, this study provides an insight in the ocean-wide storm surge properties. Nonetheless, where possible, results were compared to similar information derived from tide gauge data. Except for secular changes, the satellite-derived results are comparable to the information derived from tide gauges (correlation (> varvec{0.5})), although the tide gauges show more local variability. Where limited correlation was observed for the secular change, it was suggested that the satellites may not be able to fully capture the temporal variability in the short-lived, tropical storms, as opposed to extra-tropical storms.

The Jakarta Bay Reclamation (JBR) is a long-term protection project to prevent flooding in Jakarta. This study examines the effect of the JBR on water levels using the Regional Ocean Model (ROMS) to measure both the residual water levels (non-astronomic tide) and the total water levels generated by tides and Typhoons Hagibis and Mitag in November 2007. The results show that the tidal range in Jakarta Bay increased after the JBR, reaching 22.4% at Bekasi. The most significant amplitude change is S2 for the principal constituents and MK3 for shallow water constituents. The JBR does not change the direction of the propagation for S2 and MK3 in the Jakarta Bay, but it does change the phase lag. In addition, the JBR affects water elevations caused by tides and typhoons, with increased elevations between 2.69 and 11.53 cm. Although the aims of the land reclamation as a potential engineering solution are to provide for long-term protection against flooding from the sea, during the worst conditions (e.g., spring tides with perigee and remote forcing from typhoons), land reclamation will actually increase total water levels and amplitude of tidal constituents.