Semi-enclosed Basin Research Articles

Modelling the impact of river flow, macronutrients and solar radiation on the eutrophication status of small shallow estuaries

Small, semi-enclosed basins have often been the location of human settlements; however, this has subjected them to extensive anthropogenic use, negatively impacting the water quality and increasing their susceptibility to eutrophication. A coupled depth-averaged hydrodynamic-biogeochemical model has been configured of the shallow, microtidal Christchurch Harbour estuary, Dorset UK, to investigate processes driving declines in ecosystem health with particular emphasis on understanding the impact of changing river flows, river nutrient inputs and solar radiation. Instances of summer oxygen undersaturation and increased levels of chlorophyll were found to coincide with regions within the estuary yielding long residence times, even under low nutrient conditions. Inverse relationships between time undersaturated and both river flow and river nutrient concentration were observed but with no significant correlation between time undersaturated and solar irradiance which we attribute to the estuary's shallow nature. Our results showed that although river flow controls estuarine renewal, river nutrient concentration plays the greatest role in driving eutrophication development in small, shallow semi-enclosed basins.

Analysis of mixing structures in the Adriatic Sea using finite-size Lyapunov exponents

In this paper, we report on the mixing structures and transport properties of the Adriatic Sea surface, as a semi-enclosed basin of the Mediterranean Sea, from October 2006 until December 2011. Lagrangian transport models were used to simulate synthetic trajectories from the mean flow fields obtained by the Massachusetts Institute of Technology general circulation model implemented for the Adriatic. We examine the dispersion properties of numerical pair particles, through the calculation of time-averaged finite-size Lyapunov exponents (FSLEs) in the Adriatic Sea during selected months in each year. The results show the significant effects of river runoff and wind forcing, especially the Bora wind field, on the mixing activities of numerical pair particles by the generation of vortices, which appear as a tangle of filaments on the FSLE maps. The stretch/compression lines, which contain high values of the FSLEs, work as robust transport barriers, most having been detected along boundary currents on the eastern and western flanks of the Adriatic, particularly during winter. Numerical experiments have indicated that stable flows, with less mixing activity, occur in the northern part of the Adriatic in June and September of each year, while the Southern Adriatic Pit has flows with larger seasonal fluctuations and high values of eddy kinetic energy because of the influence of wind and energetic currents entering from the Ionian Sea.

Localized effects of offshore aquaculture on water quality in a tropical sea

Aquaculture production has increased steadily in many tropical countries over the past few decades, although impact assessments have been frequently neglected. We investigated the impacts of an offshore barramundi fish farm on water quality in the southern-central Red Sea, a traditionally understudied tropical, oligotrophic, and semi-enclosed basin. Inorganic nutrients, particulate matter, chlorophyll-a, and heterotrophic bacteria were measured periodically over 8 months around the farm. Water down-current from the farm had, on average, more heterotrophic bacteria and chlorophyll-a than up-current (11% and 34% higher, respectively). Ratios of dissolved inorganic nitrogen:phosphorus down-current from the farm were lower than ratios up-current (mean 9.8 vs 16.0, respectively). Phosphate, inorganic nitrogen, and particulate matter showed patterns of enrichment associated with the farm after a fish feeding event. Strategies such as feed optimization and considering hydrodynamics in site selection may improve water quality for future fish farms in Saudi Arabia and other tropical countries.

Dynamics-based classification of semienclosed basins

This study is guided by other classifications of estuaries that are based on specified physical constraints. Previous classifications have been relevant and revealing of diagnostic functioning of estuaries in terms of their stratification and their baroclinically induced residual circulation. Those classifications, however, have disregarded residual circulations driven by tides, not only in estuaries, but in semienclosed basins in general. The classification proposed here uses tidally averaged, or residual, dynamics. Residual dynamics are explored via drivers, or forcing agents, of residual flow. Drivers are tides or density gradients and are counteracted by ‘modifiers,’ i.e., Earth’s rotation or friction. The relative influence between forcing agents is characterized by a scaled non-dimensional densimetric tidal Froude number, Fr02, which hinges on tidal current amplitude, water depth and reduced gravity. The competition between modifiers is determined by a non-dimensional Ekman number, Ek, which depends on the kinematic eddy viscosity, the latitude and the depth of the basin. The classification suggested identifies all types of estuaries, whose dynamics is influenced by density gradients, but also recognizes frictionless tidal basins, tidal rivers, coastal lagoons, and basins that switch their dynamics from being baroclinically forced to being tidally forced. This classification can also be interpreted as an assessment of the strength of mixing (in Ek) versus the strength of baroclinicity (in Fr02), which determines the residual flows in semienclosed basins. Additionally, the classification incorporates basins forced by wind stress and/or baroclinicity, and basins forced by wind stress and/or tides.

Wave action bottom reflection source term implementation

Wave bottom reflection induced by a changing bathymetry has a major impact on the near-shore environment, where harbors and other infrastructure are based. However, this reflection is only partially accounted for in large scale numerical wave prediction models. The present work implements the analytical bottom reflection source term derived in Yevnin and Toledo (2018) to WAVEWATCH III, a numerical prediction model based on the wave action equation. The new source terms reflection coefficient magnitude, reflection direction and directional spread are shown to produce good results with respect to analytical and numerical solutions, and are tested in a real-world example. The new term allows to better simulate the near shore environment, especially near islands, reefs, semi-enclosed basins or natural beaches with long mild slopes, where the directional changes can cause previously unaccounted for effects.

The behaviors of two limnetic river plumes discharging into the semi-enclosed western basin of Lake Erie during ice-free seasons

Given the significant ecological implications of coastal plumes, their dispersion and driving mechanisms have been extensively investigated, whereas existing knowledge about the limnetic ones remain unrevealed. Accordingly, this study investigated the behaviors of the Detroit (DRP) and Maumee (MRP) River sediment plumes in the semi-enclosed western basin of Lake Erie on multiple temporal scales. Results demonstrated that the two plumes' dispersions were constrained by the basin's coastlines beyond the advections induced by Ekman currents. The north and west wind forced MRP traveled downstream, while those under the south and east wind propagated upstream. The inter-annual and seasonal variability of MRP sizes are mainly impacted by its river flux, with moderate contributions of zonal wind and the Detroit River flux, resulting in significantly larger spring patches and indicating the potential interactions between the two plumes. On the other hand, DRP paced upstream under the west wind, traveled downstream under the north and east wind, and the south wind induced advection confined it at its river mouth. Its sizes varied with wind forcing and were significantly influenced by wind directions. They had limited inter-annual variations but with prominent seasonality, which featured for small summer surface patches resulting from its negative buoyancy. Overall, this study demonstrated the behavior of two dynamically distinctive limnetic plumes bounded in a semi-enclosed basin, which could further our understanding of plume dynamics in lakes and enclosed environments.

Wind tides and surface friction coefficient in semi-enclosed shallow lagoons

The present paper is specifically focused on enclosed or semi-enclosed basins where the wind is the dominant driver of water surface tilting, leading to the so-called wind tide contributing to water levels rise. Wind-induced free surface tilting is studied using the 1-D steady form of the depth-averaged shallow water (Saint-Venant) momentum equation which reflects the depth-averaged local balance between surface slope and wind stress. Two contrasted field sites, the Berre and Vaccarès lagoons, have been monitored providing water level data along a reference axis. This study highlighted the occurrence of wind tides at the two field sites. The bimodal wind exposure ensured the robustness of the observations, with non-linear but symmetric behaviors patterns observed in winds from opposite directions. It is observed that the higher the wind speed, the steeper the slope of the free surface in accordance with the well known basic trend. In addition, a significant effect of depth is observed, with greater surface tilting in the shallower lagoon. The data analysis confirmed the robustness of such a simple approach in the present context. Using the additional assumption of constant, i.e. wind-independent, drag coefficients (CD) allowed a good match with the observations for moderate wind speeds for both sites. However, the depth effect required the CD to be increased in the shallower basin. Classical empirical wind-dependent CD parameterizations provide better wind-tide predictions than the constant-CD approach in very strong wind conditions but totally failed in predicting surface tilting in the shallower site, suggesting that physical parameters other than wind speed should be taken into account for the CD parameterization in very shallow lagoons.

\u201cGrey swan\u201d storm surges pose a greater coastal flood hazard than climate change

In this paper, we show that over the next few decades, the natural variability of mid-latitude storm systems is likely to be a more important driver of coastal extreme sea levels than either mean sea level rise or climatically induced changes to storminess. Due to their episodic nature, the variability of local sea level response, and our short observational record, understanding the natural variability of storm surges is at least as important as understanding projected long-term mean sea level changes due to global warming. Using the December 2013 North Atlantic Storm Xaver as a baseline, we used a meteorological forecast modification tool to create “grey swan” events, whilst maintaining key physical properties of the storm system. Here we define “grey swan” to mean an event which is expected on the grounds of natural variability but is not within the observational record. For each of these synthesised storm events, we simulated storm tides and waves in the North Sea using hydrodynamic models that are routinely used in operational forecasting systems. The grey swan storms produced storm surges that were consistently higher than those experienced during the December 2013 event at all analysed tide gauge locations along the UK east coast. The additional storm surge elevations obtained in our simulations are comparable to high-end projected mean sea level rises for the year 2100 for the European coastline. Our results indicate strongly that mid-latitude storms, capable of generating more extreme storm surges and waves than ever observed, are likely due to natural variability. We confirmed previous observations that more extreme storm surges in semi-enclosed basins can be caused by slowing down the speed of movement of the storm, and we provide a novel explanation in terms of slower storm propagation allowing the dynamical response to approach equilibrium. We did not find any significant changes to maximum wave heights at the coast, with changes largely confined to deeper water. Many other regions of the world experience storm surges driven by mid-latitude weather systems. Our approach could therefore be adopted more widely to identify physically plausible, low probability, potentially catastrophic coastal flood events and to assist with major incident planning.

Deep-Water Warming in the Gulf of Mexico from 2003 to 2019

AbstractA key consequence in climate change is the warming of deep waters, away from the faster warming rates of near-surface subtropical and tropical waters. Since surface and near-surface oceanic temperatures have been measured far more frequently in time and space than deep waters (>2000 m), deep measurements become quite valuable. Semi-enclosed basins, such as the Gulf of Mexico, are of particular interest as the waters below sills that connect with the neighboring oceans have residence times much longer than upper layers. Within the western Gulf of Mexico, near-bottom measurements at ~3500-m depths at four sites show a stable linear warming trend of ~16 ± 2 m°C decade−1 for the period 2007–18, and CTD data from eight oceanographic cruises occurring from 2003 to 2019 show a trend of ~18 ± ~2 m°C decade−1 from the bottom to ~2000 m below the surface. The bottom geothermal heat flux is a contributing factor to be considered in the warming and renewal of such waters, but it has not changed over millennia and is therefore unlikely to be the cause of the observed trend. The densest waters that spill into the Gulf of Mexico, over the Yucatan Channel sill, must mix substantially during their descent and in the near-bottom interior, losing their extreme values. A simple box model connects the observed warming, well within the Gulf interior, with that expected in the densest waters that spill from the North Atlantic into the Cayman Basin through Windward Passage and suggests that the source waters at the entrance to the Caribbean have been warming for at least 100 years.

Recent hydrological status of the Aegean Sea derived from free drifting profilers

Being a semi-enclosed basin of the Mediterranean Sea, the Aegean Sea comprises a complex hydrology that plays a significant role in the hydrology of the Eastern Mediterranean Sea. Its interaction with many sub-basins, along with its contribution towards the formation of deep and intermediate water, makes it an ideal case for the study of hydrological changes in transitional areas. Since 2010, the operational monitoring of the basin has been significantly enriched due to the deployment of autonomous free-drifting profilers (Argo floats) under the framework of the newly formed Greek Argo Research Infrastructure activities. In this study the hydrological status of the area is examined for the period 2010 - 2017 using the temperature and salinity profiles acquired from Argo floats that operated in the basin. The profiles are analyzed together with complementary remote sensing and model outputs datasets in order to present the spatio-temporal distribution of the co-existent water masses and shed light on hydrological features and changes that took place throughout the basin in an attempt to reassess its hydrological status during the last decade. The distribution of the physical properties in different sub-regions and their interaction is examined reconstructing a general picture of strong latitudinal gradients in the T-S and σθ fields from the upper layers towards the deeper zones. Interannually, findings indicate changes of the Aegean water masses structure within the water-column. Deep homogenization in the upper layers is recorded mainly during the winter periods of 2011-2012, 2014-2015 and 2016-2017 in the southern, central, and northern parts of the area accordingly. The observed dense water formation events, along with mixing and advection appear to alterate the water column physical properties structure and affect the dynamics of the surface and sub-surface dominant water masses in the Aegean. The results further highlight the valuable information that can be extracted from the operation of free-drifting profilers in enclosed marginal seas similar to the Aegean case.

Spread of the non-indigenous ascidian Aplidium accarense (Millar, 1953) in the Eastern Mediterranean Sea: morphological and molecular tools for an accurate identification

The aplousobranch ascidian Aplidium accarense (Millar, 1953) was first described on the western coast of Africa, where it is considered native. Afterwards, this species was introduced along south-American Atlantic coasts, where it affected local shellfish farms through a massive colonization of both natural and artificial substrata. Aplidium accarense has been recently reported along Catalan coasts and in the Tyrrhenian Seas (Western Mediterranean) where it represents a non-indigenous species, only recorded in harbours and aquaculture farms thus far. These Mediterranean records support the hypothesis that A. accarense is currently expanding within the basin, representing a potential invasive species. In this study, several colonies of A. accarense were found for the first time on artificial substrata within the semi-enclosed basin of the Mar Piccolo of Taranto (Italy, Ionian Sea), in the Eastern Mediterranean. Here we provide an updated description of A. accarense combining both morphological and molecular approaches, in order to allow an accurate and reliable identification of this expanding species. Comparing the morphology of the specimens collected from Taranto with the previous descriptions, a slight intra-specific variability has been noticed. Therefore, we provide detailed comparisons of the specimens found in Taranto with all the other A. accarense sampled in other areas of the world, in order to highlight the intra-species variability. The correct identification of a potentially-dangerous species such as A. accarense, represents a needed step for environmental monitoring purposes and for implementing management strategies to mitigate the effects of non-indigenous species on natural ecosystems and human activities.

An Evaluation of the Main Physical Features and Circulation Patterns in the Black Sea Basin

Having as target the semi-enclosed basin of the Black Sea, the main purpose of the present paper is to provide an overview of its general physical features and circulation patterns. In order to achieve this goal, more than five decades of data analysis – from 1960 to 2015 – were taken into consideration and the results were checked against known data, both from satellite data over the last two decades and in-situ measurements from earlier decades. The circulation of the Black Sea basin has been studied for almost 400 years, since the Italian Count Luigi Marsigli first described the ‘two layer’ circulation through the Bosphorus Strait in the year 1681. Since climate change projections for the Black Sea region foresee significant impact on the environment in the coming decades, a set of adaptation and mitigation measures is required, therefore more research is needed. Nowadays, the warming trend adds a sense of immediate urgency because according to the National Oceanic and Atmospheric Administration’s National Centre for Environmental Information, July 2020 was the second-hottest month ever recorded for the planet. Its averaged land and ocean surface temperature tied with July 2016 as the second-highest for the month in the 141-year NOAA’s global temperature dataset record, which dates back to 1880. It was 0.92°C above the 20th-century average of 15.8°C, with only 0.01°C less than the record extreme value measured in July of 2019.

Geomorphology of Canyon Outlets in Zrmanja River Estuary and Its Effect on the Holocene Flooding of Semi-enclosed Basins (the Novigrad and Karin Seas, Eastern Adriatic)

Detailed multi-beam bathymetry, sub-bottom acoustic, and side-scan sonar observations of submerged canyons with tufa barriers were used to characterize the Zrmanja River karst estuary on the eastern Adriatic coast, Croatia. This unique karst environment consists of two submerged karst basins (Novigrad Sea and Karin Sea) that are connected with river canyons named Novsko Ždrilo and Karinsko Ždrilo. The combined use of high-resolution geophysical data with legacy topography and bathymetry data in a GIS environment allowed for the description and interpretation of this geomorphological setting in relation to the Holocene sea-level rise. The tufa barriers had a predominant influence on the Holocene flooding dynamics of the canyons and karst basins. Here, we describe the possible river pathways from the basins during the lowstand and the formation of a lengthening estuary during the Holocene sea-level rise. Based on the analyzed morphologies and the relative sea-level curve for the Adriatic Sea, the flooding of the Novsko Ždrilo occurred 9200 years before present (BP) and Karinsko Ždrilo was flooded after 8400 years BP. The combination of high-resolution geophysical methods gave an accurate representation of the karst estuarine seafloor and the flooding of semi-isolated basins due to sea-level rise.

Near-Surface Transport Properties and Lagrangian Statistics during Two Contrasting Years in the Adriatic Sea

This paper describes the near-surface transport properties and Lagrangian statistics in the Adriatic semi-enclosed basin using synthetic drifters. Lagrangian transport models were used to simulate synthetic trajectories from the mean flow fields obtained by the Massachusetts Institute of Technology general circulation model (MITgcm), implemented in the Adriatic from October 2006 until December 2008. In particular, the surface circulation properties in two contrasting years (2007 had a mild winter and cold fall, while 2008 had a normal winter and hot summer) are compared here. In addition, the Lagrangian statistics for the entire Adriatic Basin after removing the Eulerian mean circulation for numerical particles were calculated. The results indicate that the numerical particles were slower in this simulation when compared with the real drifters. This is because of the reduced energetic flow field generated by the MIT general circulation model during the selected years. The numerical results showed that the balanced effects of the wind-driven recirculation in the northernmost area(which would be a sea response to the Bora wind field) and the Po River discharge cause the residence times to be similar during the two selected years (182 and 185 days in 2007 and 2008, respectively). Furthermore, the mean angular momentum, diffusivity, and Lagrangian velocity covariance values are smaller than in the real drifter observations, while the maximum Lagrangian integral time scale is the same.

Object-Based Modeling of Marine Phytoplankton and Seaweeds

The aim of this work is to simulate the dissolved oxygen deficiency in the coastal zone that sometimes occurs during the summer water stagnation. We consider the main components of the marine ecosystem that play a major role in such processes—concentrations of nitrogen, phosphorus and sulfur compounds in water, dissolved and particular organic matter, oxygen, biomass of phytoplankton and macroalgae. We use the object-based modeling technique to simulate the spatio-temporal variability of the ecosystem in a 2D domain. In comparison with the traditional approach, it gives several advantages: more precise parametrizations of the biological components’ functionality; higher spatial resolution; possibility to account for the individual variability of hydrobionts; easy inclusion of an arbitrary number of species in the model. Our model included three species of phytoplankton and seven macroalgae. Individual-based modules control their functionality. Species of phytoplankton and seaweeds chosen for simulations are typical for the coastal zone of Crimea. In the simulations, we study the contribution of micro- and macroalgae to the processes of self-purification of a semi-enclosed basin in case of a sharp increase in nutrient concentration in water.

Lagrangian modelling of a person lost at sea during the Adriatic scirocco storm of 29 October 2018

Abstract. On 29 October 2018 a windsurfer's mast broke about 1 km offshore from Istria during a severe scirocco storm in the northern Adriatic Sea. He drifted in severe marine conditions until he eventually beached alive and well in Sistiana (Italy) 24 h later. We conducted an interview with the survivor to reconstruct his trajectory and to gain insight into his swimming and paddling strategy. Part of survivor's trajectory was verified using high-frequency radar surface current observations as inputs for Lagrangian temporal back-propagation from the beaching site. Back-propagation simulations were found to be largely consistent with the survivor's reconstruction. We then attempted a Lagrangian forward-propagation simulation of his trajectory by performing a leeway simulation using the OpenDrift tracking code using two object types: (i) person in water in unknown state and (ii) person with a surfboard. In both cases a high-resolution (1 km) setup of the NEMO v3.6 circulation model was employed for the surface current component, and a 4.4 km operational setup of the ALADIN atmospheric model was used for wind forcing. The best performance is obtained using the person-with-a-surfboard object type, giving the highest percentage of particles stranded within 5 km of the beaching site. Accumulation of particles stranded within 5 km of the beaching site saturates 6 h after the actual beaching time for all drifting-particle types. This time lag most likely occurs due to poor NEMO model representation of surface currents, especially in the final hours of the drift. A control run of wind-only forcing shows the poorest performance of all simulations. This indicates the importance of topographically constrained ocean currents in semi-enclosed basins even in seemingly wind-dominated situations for determining the trajectory of a person lost at sea.

An investigation of mass changes in the Bohai Sea observed by GRACE

The Gravity Recovery and Climate Experiment (GRACE) satellite mission has profoundly advanced our knowledge of contemporary sea level change. Owing to the coarse spatial resolution and leakage issue across the land–ocean boundary, it is challenging (even impossible) for GRACE to detect mass changes over a region smaller than its spatial resolution, especially a semi-enclosed basin (e.g., the Bohai Sea) that is adjacent to land with significant mass variation. In this contribution, the causes for the GRACE RL06 mass changes in the Bohai Sea are investigated using a reconstruction technique that is implemented with multisource data, including altimeter observations, steric estimates, and land mass changes from GRACE RL06 mascon solution. Our results by the reconstruction technique demonstrate that the GRACE annual cycles are primarily caused by water mass changes rather than sediment changes. On the other hand, the mass trends from both reconstructed signals and those observed by the GRACE RL06 spherical harmonic coefficients (SHCs) are small, ranging from − 0.38 mm/year to 0.51 mm/year (depending on different data sources). Given that our estimated accuracies are > 0.8 mm/year (the real accuracies should be larger), our reconstructed results cannot directly confirm the presence of sediment accumulation or water mass increase; however, analysis of only the altimetry data suggests the mass trends are due to water mass increase, which would amount to ~ 0.44 Gt/year. Further investigation suggests that the mass trends in the Bohai Sea suffer from a − 2.9 mm/year leakage-in effect from groundwater depletion in the North China and about 2.5 mm/year signal attenuation (resulting in a ~ 2.5 mm/year remaining trend that is roughly equivalent to the leakage-in trend, consequently leading to the small mass trend in the Bohai Sea). Our reconstruction results exemplify that elaborate data processing is necessary for specific cases. We also test whether the recently released RL06 mascon solutions that are resolved with constraints and require no further processing would improve the agreement with altimeter observations. We find that the seasonal cycles are improved relative to the RL06 SHCs; however, the rates derived from the mascon solutions cannot properly represent the altimeter-derived ocean mass estimates for the Bohai Sea, probably because the mascon solutions underestimate the rates or contain some processing artifacts. Nevertheless, the mascon solutions show enhanced signals, which offer new opportunities to investigate regional sea level change.

Radium Mass Balance Sensitivity Analysis for Submarine Groundwater Discharge Estimation in Semi-Enclosed Basins: The Case Study of Long Island Sound

Estimation of submarine groundwater discharge (SGD) to semi-enclosed basins by Ra isotope mass balance is herein assessed. We evaluate 224Ra, 226Ra and 228Ra distributions in surface and bottom waters of Long Island Sound (CT-NY, USA) collected during spring 2009 and summer 2010. Surface water and bottom water Ra activities display an apparent seasonality, with greater activities during the summer. Long-lived Ra isotope mass balances are highly sensitive to boundary fluxes (water flux and Ra activity). Variation (50%) in the 224Ra, 226Ra and 228Ra offshore seawater activity results in a 63 – 74% change in the basin-wide 226Ra SGD flux and a 58 – 60% change in the 228Ra SGD flux, but only a 4 – 9% change in the 224Ra SGD flux. This highlights the need to accurately constrain long-lived Ra activities in the inflowing and outflowing water, as well as water fluxes across boundaries. Short-lived Ra isotope mass balances are sensitive to internal Ra fluxes, including desorption from resuspended particles and inputs from sediment diffusion and bioturbation. A 50% increase in the sediment diffusive flux of 224Ra, 226Ra and 228Ra results in a ~30% decrease in the 224Ra SGD flux, but only a ~6 – 10% decrease in the 226Ra and 228Ra SGD flux. When boundary mixing is uncertain, 224Ra is the preferred tracer of SGD if sediment contributions are adequately constrained. When boundary mixing is well-constrained, 226Ra and 228Ra are the preferred tracers of SGD, as sediment contributions become less important. A three-dimensional numerical model is used to constrain boundary mixing in Long Island Sound, with mean SGD fluxes of 1.2 ± 0.9 *1013 L y-1 during spring 2009 and 3.3 ± 0.7 *1013 L y-1 during summer 2010. The SGD flux to Long Island Sound during summer 2010 was one order of magnitude greater than the freshwater inflow from the Connecticut River. The maximum marine SGD-driven N flux is 14 ± 11 *108 mol N y-1 and rivals the N load of the Connecticut River.

Looking for an Offshore Low-Level Jet Champion among Recent Reanalyses: A Tight Race over the Baltic Sea

With an increasing interest in offshore wind energy, focus has been directed towards large semi-enclosed basins such as the Baltic Sea as potential sites to set up wind turbines. The meteorology of this inland sea in particular is strongly affected by the surrounding land, creating mesoscale conditions that are important to take into consideration when planning for new wind farms. This paper presents a comparison between data from four state-of-the-art reanalyses (MERRA2, ERA5, UERRA, NEWA) and observations from LiDAR. The comparison is made for four sites in the Baltic Sea with wind profiles up to 300 m. The findings provide insight into the accuracy of reanalyses for wind resource assessment. In general, the reanalyses underestimate the average wind speed. The average shear is too low in NEWA, while ERA5 and UERRA predominantly overestimate the shear. MERRA2 suffers from insufficient vertical resolution, which limits its usefulness in evaluating the wind profile. It is also shown that low-level jets, a very frequent mesoscale phenomenon in the Baltic Sea during late spring, can appear in a wide range of wind speeds. The observed frequency of low-level jets is best captured by UERRA. In terms of general wind characteristics, ERA5, UERRA, and NEWA are similar, and the best choice depends on the application.

Reconstruction of Holocene oceanographic conditions in eastern Baffin Bay

Abstract. Baffin Bay is a semi-enclosed basin connecting the Arctic Ocean and the western North Atlantic, thus making out a significant pathway for heat exchange. Here we reconstruct the alternating advection of relatively warmer and saline Atlantic waters versus the incursion of colder Arctic water masses entering Baffin Bay through the multiple gateways in the Canadian Arctic Archipelago and the Nares Strait during the Holocene. We carried out benthic foraminiferal assemblage analyses, X-ray fluorescence scanning, and radiocarbon dating of a 738 cm long marine sediment core retrieved from eastern Baffin Bay near Upernavik, Greenland (Core AMD14-204C; 987 m water depth). Results reveal that eastern Baffin Bay was subjected to several oceanographic changes during the last 9.2 kyr. Waning deglacial conditions with enhanced meltwater influxes and an extensive sea-ice cover prevailed in eastern Baffin Bay from 9.2 to 7.9 ka. A transition towards bottom water amelioration is recorded at 7.9 ka by increased advection of Atlantic water masses, encompassing the Holocene Thermal Maximum. A cold period with growing sea-ice cover at 6.7 ka interrupts the overall warm subsurface water conditions, promoted by a weaker northward flow of Atlantic waters. The onset of the neoglaciation at ca. 2.9 ka is marked by an abrupt transition towards a benthic fauna dominated by agglutinated species, likely in part explained by a reduction of the influx of Atlantic Water, allowing an increased influx of the cold, corrosive Baffin Bay Deep Water originating from the Arctic Ocean to enter Baffin Bay through the Nares Strait. These cold subsurface water conditions persisted throughout the Late Holocene, only interrupted by short-lived warmings superimposed on this cooling trend.