Sea Interior Research Articles

Emerging Influence of Enhanced Greenland Melting on Boundary Currents and Deep Convection Regimes in the Labrador and Irminger Seas

AbstractFreshwater input from Greenland ice sheet melt has been increasing in the past decades from warming temperatures. To identify the impacts from enhanced meltwater input into the subpolar North Atlantic from 1997 to 2021, we use output from two nearly identical simulations in the eddy‐rich model VIKING20X (1/20°) only differing in the freshwater input from Greenland: one with realistic interannually varying runoff increasing in the early 2000s and the other with climatologically (1961–2000) continued runoff. The majority of the additional freshwater remains within the boundary current enhancing the density gradient toward the warm and salty interior waters yielding increased current velocities. The accelerated boundary current shows a tendency to enhanced, upstream shifted eddy shedding into the Labrador Sea interior. Further, the experiments allow to attribute higher stratification and shallower mixed layers southwest of Greenland and deeper mixed layers in the Irminger Sea, particularly in 2015–2018, to the runoff increase in the early 2000s.

Decadal variability of eddy temperature fluxes in the Labrador Sea

Small-scale eddies play an important role in preconditioning and restratifying the water column before and after mixing events, thereby affecting deep water formation variability. Results from a realistic eddy-resolving (∼5 km local horizontal resolution) ocean model suggest that small-scale temperature fluxes due to turbulent potential to kinetic energy conversion are the main driver of mixed layer restratification during deep convection in the Labrador Sea interior and the West Greenland Current. This resupply of heat due to turbulent upward buoyancy fluxes exhibits a large interannual variability imposed by the atmospheric forcing. Eddy fluxes only become active in periods of strong buoyancy loss, while being quiescent otherwise. In a low-resolution (∼20 km) control simulation the modeled turbulence is strongly reduced and the associated modeled and parameterized heat fluxes are too weak to increase stratification.

How do topography and thermal front influence the water transport from the northern Laotieshan Channel to the Bohai Sea interior in summer?

Water renewal through the Bohai Strait largely dominates the water quality of the semi-enclosed Bohai Sea (BS), which connects only to the northern Yellow Sea (NYS) through the strait. Although the peak water transport through the Bohai Strait occurs in summer, the spatially averaged water residence time of the BS shows no significant decrease compared to other periods. A three-dimensional model is applied to unravel the detailed structure and dynamic processes of the summertime NYS water transport from the northern Laotieshan Channel to the BS interior. Model results from both climatological and hindcasting cases show that despite a large amount of the NYS water enters the strait, they are confined to the Laotieshan Channel between the Central Bank and Dalian surrounded by a strong Ω-shaped tidal front and could not move further north into the Liaodong Bay. The strong along-front flow steered by the topography forms a counter-clockwise circulation pattern in the strait zone, resulting in most of water southward movement east of the Central Bank, then join the outflow south of the strait and leave for the NYS. The Central Bank and the topographic sill north of the Laotieshan Channel act as a barrier that significantly reduces the water exchange between the strait zone and the BS interior, in particular the Liaodong Bay. Particle-tracking experiments suggest that less than 10% of particles released in the NYS could finally reach the BS interior, and among of them only a small portion of them could move further north into the Liaodong Bay. Momentum diagnostics suggest that the water transport northwest of the strait is dominated by geostrophic balance in the Ω-shaped frontal region. Sensitivity experiments indicate that tides promote the surface water transport from the NYS to the BS interior. The realistic wind forcing including synoptic events may facilitate the water transport from the strait to the BS interior by modulating the barotropic and baroclinic pressure gradient than that with the climatological wind case.

Carbon cycling in the East Sea (Japan Sea): A review

The East Sea (also known as the Japan Sea; hereafter, EJS) is a semi-enclosed marginal sea surrounded by the Korean Peninsula, Russia, and the Japanese Islands. The EJS is connected to the Pacific through shallow straits. Thus, the EJS has its own thermohaline circulation and the characteristic biogeochemistry. The deep overturning circulation plays a critical role in carbon cycling including absorption of atmospheric CO2 and its sequestration into the interior of the sea. The turnover time of the deep EJS (>1000 m) is ~ hundred years and probably varies depending on physical climate forcing. Thus, the effect of climate change on oceanic processes may be more easily detected in the EJS. In this paper, we summarize the current understanding of carbon cycling in the EJS. We focus especially on the Ulleung Basin in the southwestern EJS, from which more extensive data are available. Notable features of carbon cycling in the EJS include the following: primary productivity and the export/production ratio are higher than in the adjacent Pacific; the EJS is a net sink of atmospheric CO2 and anthropogenic CO2 content is ~1% of the dissolved inorganic carbon inventory; dissolved inorganic carbon in the sea interior is mostly supplied by organic matter decomposition rather than CaCO3 dissolution and thus, the deep waters are vulnerable to acidification; N:P molar ratio of the deep waters is ~13, lower than the Redfield ratio; concentration of dissolved organic carbon is significantly higher than in the oceans; and sediment resuspension and lateral transport is an important component of sinking particulate organic carbon (POC) flux. Another important feature is the temporal trends observed for the last few decades. For example, pH, calcium carbonate saturation status, and dissolved oxygen concentration in the sea interior have decreased, whereas dissolved inorganic carbon and likely, the inventory of anthropogenic CO2 have increased. These temporal trends have an implication on better understanding of the processes occurring more slowly in the oceans. Brief suggestions for future research that will improve our understanding of carbon cycling and its variability are provided at the end of the paper.

Frontal Dynamics in the Alboran Sea: 2. Processes for Vertical Velocities Development

AbstractSignificant lateral density gradients occur throughout the year in the Alboran Sea, giving rise to two main fronts: the Western Alboran Gyre Front (WAGF) and Eastern Alboran Gyre Front (EAGF), where large vertical velocities often develop. To improve the understanding of the processes that underlie the development of the vertical velocities in the fronts, the periods of development were analyzed in the perspective of the frontogenesis, instabilities, non‐linear Ekman, and filamentogenesis mechanisms, using multi‐platform in‐situ observations and a high‐resolution realistic simulation in spring 2018. The spatio‐temporal characteristics of the WAGF indicate a wider, deeper, and longer‐lasting front than the EAGF. Additionally, the WAGF shows stronger and deeper upwelling and downwelling regions. The WAGF vertical velocities (up to |55| m/day) are amplified by an across‐front ageostrophic secondary circulation generated by: (a) frontal intensification explained by frontogenesis, which shows a sharpening of buoyancy gradients associated with the Atlantic Jet, (b) nonlinear Ekman effects, that are enhanced by the persistent western wind blowing along the frontal direction, and (c) submesoscale instabilities (symmetric and ageostrophic baroclinic instabilities). The EAGF vertical velocities (up to |38| m/day) are amplified by two asymmetrical ageostrophic cells developed across the front with a narrow upwelling region in the middle. The cell's circulation is explained by frontal intensification produced by filamentogenesis through a cold filament advection to the Mediterranean Sea interior, that is characterized by pointy isopycnals at the center of the filament. This mechanism is observed in both the model and glider observations.

The Effects of Atmospheric and Lateral Buoyancy Fluxes on Labrador Sea Mixed Layer Depth

The depth of the Labrador Sea mixed layer during winter convection is a balance between atmospheric buoyancy loss and lateral buoyancy exchange, and is notoriously difficult to represent accurately in ocean and climate models. This study shows that lateral exchanges of heat and salt between the shelf and the interior are smaller in a regional coupled ocean–sea ice model at higher vertical resolution (75 levels compared with 50 levels), due in part to altered bathymetry along the Greenland shelf. Reduced lateral exchange results in a stronger stratification in the interior of the Labrador Sea, with stronger convection resistance which results in unrealistically shallow mixed layers. The westward fluxes of heat and salt associated with Irminger Water at Cape Farewell are 50 % and 33 % lower, respectively, with higher vertical resolution. Exchanges south of the Labrador Sea from the North Atlantic Current are also smaller, contributing to a reduction in salt and heat import into the Labrador Sea interior. When the high resolution model is forced with a stronger wintertime buoyancy loss at the ocean surface, this weakens the Labrador Sea stratification, allowing the forcing to break through the freshwater cap and increasing convection, bringing mixed layer depths back to observed values. A strong atmospheric forcing can therefore compensate for a reduction in lateral advection. The mixed layer depths, which are representative of convection and Labrador Sea water formation, will be the focus in this study. Therefore, this study suggests that convection and Labrador Sea Water formation is a complex interplay of surface and lateral fluxes, linked to stratification thresholds.

Advective pathways and transit times of the Red Sea Overflow Water in the Arabian Sea from Lagrangian simulations

The present study investigates the advective pathways and transit times of virtual particles released in the Red Sea outflow area as a proxy for the poorly understood spreading of the Red Sea Overflow Water (RSOW) in the Arabian Sea. This work uses the Parcels toolbox, a Lagrangian framework, to simulate tens of thousands of trajectories under different initial conditions. Six different Lagrangian simulations are performed at isobaric and isopycnal surfaces within the RSOW layer. All simulations are based on the eddy-rich GLORYS12 reanalysis that merges almost all in-situ (temperature–salinity) and satellite observations collected over the last two decades into a dynamical framework. This study shows that GLORYS12 reproduces relatively well the climatological seasonal cycle of the RSOW to the Gulf of Aden and essential characteristics of the exchange at the Strait of Bab al-Mandab. Statistical comparisons between synthetic trajectories and RAFOS floats in the Gulf of Aden corroborate the quality of GLORYS12 velocity fields used for the Lagrangian simulations. Six main advective pathways are uncovered (by order of preference): Southwest, Northwest, Socotra Passage, Central, Eastern, and Southern. Trajectories from Argo floats give observational support for some of these paths. Although most particles are exported out of the Arabian Sea off Somalia, the simulations reveal robust connectivity of the RSOW to the Arabian Sea interior and its eastern boundary. The fact that particles have long trajectories in the interior increases the potential of RSOW mixing with the fresher and oxygen-poor ambient waters. Thus, these pathways may have profound implications for the salt and oxygen budgets in the Arabian Sea and beyond since the RSOW is also part of the global overturning circulation and exported out of the Indian Ocean via the Agulhas Current. Transit time distributions indicate that it takes about six months for outflow-originated particles to spread over the entire Gulf of Aden and one to three years to be exported along the western boundary, toward Somalia (Socotra Passage and Southwest pathways) and off the Yemeni–Omani coast (Northwest Pathway). In contrast, reaching the eastern boundary takes much longer. North of 14°N, the most frequent time is around 10–15 years, and about 20–25 years at the southeastern Arabian Sea. Hence, the RSOW can often carry oxygen to the western boundary but not to the eastern basin. This may contribute to the eastern shift of the Arabian Sea Oxygen Minimum Zone, a subject that deserves investigation.

Submesoscale modulation of deep water formation in the Labrador Sea

Submesoscale structures fill the ocean surface, and recent numerical simulations and indirect observations suggest that they may extend to the ocean interior. It remains unclear, however, how far-reaching their impact may be—in both space and time, from weather to climate scales. Here transport pathways and the ultimate fate of the Irminger Current water from the continental slope to Labrador Sea interior are investigated through regional ocean simulations. Submesoscale processes modulate this transport and in turn the stratification of the Labrador Sea interior, by controlling the characteristics of the coherent vortices formed along West Greenland. Submesoscale circulations modify and control the Labrador Sea contribution to the global meridional overturning, with a linear relationship between time-averaged near surface vorticity and/or frontogenetic tendency along the west coast of Greenland, and volume of convected water. This research puts into contest the lesser role of the Labrador Sea in the overall control of the state of the MOC argued through the analysis of recent OSNAP (Overturning in the Subpolar North Atlantic Program) data with respect to estimates from climate models. It also confirms that submesoscale turbulence scales-up to climate relevance, pointing to the urgency of including its advective contribution in Earth systems models.

Influence of Sediment Resuspension on the Biological Pump of the Southwestern East Sea (Japan Sea)

The biological carbon pump in the southwestern East Sea (Japan Sea, EJS hereafter) was investigated based on examination of sinking particulate matter samples intercepted by bottom-tethered sediment traps deployed on a mooring at three depths (500, 1000, and 2000 m) between 2011 and 2017. The total particle flux increased as the sampling depth increased, while particulate organic carbon (POC) flux was greatest at 500 m. The lithogenic material content was high at all depths, and accounted for an average of ~42 % of the particulate matter. The total particle flux at all sampling depths consistently shifted towards much higher values in 2014-2016. During this period, the POC flux at 500 m increased by 32 % while net primary production (NPP) increased only slightly. Consequently, the POC flux/NPP ratio increased significantly, indicating greater biological pump efficiency than in earlier years of the study. The flux of lithogenic material derived primarily from sediment resuspension was much greater at 500 m in 20142016 compared with previous years, implying its potential role as a ballast mineral in enhancing particle export and transfer to the deep sea interior. The radiocarbon isotope ratio of POC was higher, and the excess Mn content values were lower at 500 m in 2014-2016, suggesting that the resuspended sediment at 500 m likely originated from a shallow region during this period, and differed in provenance from the lithogenic material intercepted at 2000 m. The period of enhanced particle flux coincided with the 2015/16 El Nino and a mesoscale warm (anticyclonic) eddy that persisted for two years in the study region. The East Korean Warm Current and the eddy may have facilitated the transport of resuspended particles entrained in the Korea Strait and/or the western shelf and upper slope of the basin to the study site.

Regional climate and patterns of phytoplankton annual succession in the open waters of the Black Sea

The annual succession of phytoplankton of the open waters of the Black Sea was investigated on the basis of a database covering the 30-year period from 1985 to 2014. Seasonal variations of the taxonomic composition were analysed with regard to weather conditions and the physical and chemical properties of the environment. Two different patterns of annual phytoplankton succession were revealed for the post-winter period from March to November. After cold winters a classical annual succession of diatoms → dinoflagellates → coccolithophores → dinoflagellates → diatoms was observed, whereas after regular winters another type of succession; dinoflagellates → dinoflagellates → coccolithophores → diatoms → diatoms, took place. These two successions corresponded to seasonal dynamics of nitrate concentration and its share in the total inorganic nitrogen. During cold years these parameters decreased from spring to summer with a subsequent increase in autumn, whereas in regular years they were unusually high in summer. The enigma of this summer nitrate enrichment is well explained by the hypothesis of increasing cross-shelf nutrient transport. During regular years, weak hydrodynamic forcing occurs throughout the year, resulting in a large number of mesoscale eddies along the shelf in summer–autumn that in turn cause the intense transport of coastal waters rich in nitrate to the Sea interior. Development of the large-celled diatom Pseudosolenia calcar-avis in the sea basin observed in summer is in line with this hypothesis. This mechanism was also confirmed by positive relationships between the high sea-surface temperature, and the low Ekman pumping velocity and mean kinetic energy of currents in winter on the one hand, and the contribution of diatoms to the total phytoplankton biomass in summer–autumn, on the other. A case study of mesoscale eddies in the open waters in summer–autumn demonstrated a shift in species composition to large-celled diatoms inside these structures. Climate warming observed during the last 25 years resulted in a decrease in the frequency of cold winters from 30% to 15%, which has led to a decline in the annual phytoplankton standing stock. Thus, in the Black Sea, climate warming affects phytoplankton not directly by an increase in temperature, but by a decrease in the frequency of cold winters.

Observation and analysis of tidal and residual current in the North Yellow Sea in the spring

In order to study the current characteristics of the North Yellow Sea (NYS), 4 moored ADCPs (Acoustic Doppler Current Profilers) were deployed and Current characteristics were analyzed based on the observations. Results show that tidal current is the dominant and M2 is the main constituent. Shallow water constituents are obvious in the near-shore area, and tidal current ellipses directions have relations with topography. Residual currents in the Bohai Strait point to the Bohai Sea interior and the magnitude have a connection with terrain. Residual current in south NYS can be divided into two layers, and energy of residual current only accounts for about 13% of the total energy. Barotropic eddy kinetic energy plays a major role and the average in NYS accounts for 87%, baroclinic mean kinetic energy is larger in north NYS, in other regions barotropic mean kinetic energy take the leading position.

Sun-stirred Kraken Mare: Circulation in Titan’s seas induced by solar heating and methane precipitation

Density-driven circulation in Titan’s seas forced by solar heating and methane evaporation/precipitation is simulated by an ocean circulation model. If the sea is transparent to sunlight, solar heating can induce anti-clockwise gyres near the sea surface and clockwise gyres near the sea bottom. The gyres are in geostrophic balance between the radially symmetric pressure gradient force and Coriolis force. If instead the sea is turbid and most sunlight is absorbed near the sea surface, the sea gets stratified in warm seasons and the circulation remains weak. Precipitation causes compositional stratification of the sea to an extent that the sea surface temperature can be lower than the sea interior temperature without causing a convective overturning. Non-uniform precipitation can also generate a latitudinal gradient in the methane mole fraction and density, which drives a meridional overturning with equatorward currents near the sea surface and poleward currents near the sea bottom. However, gyres are more ubiquitous than meridional overturning.

Varying temperature and heat content signatures in the central Labrador Sea at different layers and timescales

The dominant modes of variability in the temperature and ocean heat content (OHC; 0–1000m) of the central Labrador Sea were investigated using the Hilbert–Huang Transform (HHT) based on Argo profiles collected during 2003–2012. Warming trends of approximately 0.03°Cyr−1 were observed in the upper 2000m of the water column. A strong annual temperature cycle exists and dominates at the 500m depth, while signals at the interannual timescales can explain most of the temperature variability at the 1000m and 1500m depths. These interannual signals are closely correlated to the variability of deep convection in the Labrador Sea, which has intermittent enhancement of mixed layer depth (MLD)>1500m. The Hilbert spectrum from the OHC in the Labrador Sea interior reveals two important components at frequencies of 0.8−1.2cycleyr−1 (T=0.8–1.25 years) and 0.1−0.3cycleyr−1 (T=3.3–10 years), respectively, superimposed on the warming trends. The former corresponds to the dominant seasonal cycle due to surface heating, while the latter is concomitant with the timing of the reoccurrence of convective events. We also found that the cumulative North Atlantic Oscillation (NAO) index significantly correlates to the low-frequency OHC variations. Therefore, the interannual signals in the Labrador Sea at especially the intermediate layers are attributed to changes in the deep convective processes and the atmospheric conditions. By comparing with an extended OHC record (1945–2010), it was further shown that the warming trends obtained from the 10-year Argo record are part of multi-decadal variations that presumably reflect the Atlantic Multi-decadal Oscillation (AMO). In addition, the recent OHC changes in the Labrador Sea (i.e., increased heat in the deeper layers) may be related to the current global warming hiatus, suggesting the potential contributions from the Atlantic Meridional Overturning Circulation (AMOC) to the low-frequency OHC in the Labrador Sea.

Alternation of diatoms and coccolithophores in the north-eastern Black Sea: a response to nutrient changes

In many regions phosphorus limits coccolithophore growth, whereas nitrogen generally controls development of diatoms. We tested the hypothesis that a change in nutrient composition defines the alternation of these algae. Data on phytoplankton, nutrients, chlorophyll and primary production were obtained in May–June from 2002 to 2012. Coccolithophore bloom dynamics were analysed using satellite images of particular inorganic carbon (PIC). In some years coccolithophore bloom occupied the sea interior and has spread on shelf areas. Most frequently blooms occurred in the coastal waters and were absent in the deep basin. Diatoms and coccolithophores interchangeably prevailed in phytoplankton. In the coastal waters, high biomass of diatoms corresponded to the increased ammonium. In the deep basin, PIC was positively correlated with phosphate and negatively with the sea air temperature in February indicating that the bottom-up flux of pycnocline waters during winter convection is the main driver of coccolithophore bloom. In the coastal zone, high concentrations of phosphate and PIC corresponded to high precipitation periods. Thus, independent from origin, phosphorus might have determined the development of coccolithophores both in the coastal and deep waters. In general, diatoms predominated in phytoplankton at high nitrogen:phosphorus ratio, whereas coccolithophores at low.

An objective reconstruction of the Mediterranean sea carbonate system

An objective estimation of the current distribution of carbonate system variables for the Mediterranean Sea is proposed using empirical relationships derived from ship-based observations and combined with monthly climatological fields of hydrographic parameters. The high quality data of METEOR84/3 cruise were used to fit multiple linear regression models of Dissolved Inorganic Carbon (DIC) and Total Alkalinity (TA) from other hydrochemical parameters. These algorithms provided a robust estimation of DIC and TA, with corresponding Root Mean Squared Errors of 7.66 and 5.09µmol/kg, by accounting only for potential temperature, salinity, pressure, and nitrate concentration. After the application of the identified regression models to a set of publicly available climatological fields, an objective assessment of the reconstructed carbonate system monthly distributions was derived and compared against different ship-based surveys. Results showed that the Mediterranean Sea interior was well reproduced with errors <14µmol/kg, whereas the near surface layers still exhibited large uncertainties. The lower degree of confidence of this approach at the surface does not allow the direct application for studying anthropogenic CO2 trends, but some qualitative considerations were drawn from the comparison between the estimated inorganic carbon system and the available observational datasets. Most importantly, the present work showed that the estimated inventories are able to capture the linkages with the physical oceanic features of the system and we propose this method as an inexpensive solution to support the design of monitoring activities in the Mediterranean Sea, which is still poorly constrained by direct observations.

Intrusion of low-salinity water into the Yellow Sea Interior in 2012

Abnormally low-salinity water was detected in the surface layer of the central region of the Yellow Sea in August 2012. The presence of such low-salinity water in the Yellow Sea interior has never been reported previously. To understand the origin of this low-salinity water, oceanographic and wind data were analyzed, and the circulation of the surface layer was also examined in the Yellow and East China Seas using a numerical ocean model. The results confirmed that typhoons caused the low-salinity water. Two consecutive typhoons passed from east to west across the East China Sea, around the Changjiang Bank in early August 2012. Strong easterly and southeasterly winds created by the typhoons in the Yellow and East China Seas drove the low-salinity water to the north along the coast of China and northeastward toward the central region of the Yellow Sea, respectively. Usually, the northward drifting of Changjiang Diluted Water along the coast of China ends around the Jiangsu coast, where the drifting is blocked and is turned by the offshore Eulerian residual current. Therefore, the Changjiang Diluted Water does not intrude more into the Yellow Sea interior. However, in 2012, the low-salinity water drifted up to the Shandong Peninsula along the coast of China, and formed massive low-salinity water in the Yellow Sea interior combining with the other low-salinity water extended toward the central region of the Yellow Sea directly from the Changjiang Bank. Thus, the typhoons play a key role in the appearance of abnormally low-salinity water in the Yellow Sea interior and it means that the Yellow Sea ecosystem could be significantly influenced by the Changjiang Diluted Water.

Boundary mixing in Orkney Passage outflow

AbstractOne of the most remarkable features of contemporary oceanic climate change is the warming and contraction of Antarctic Bottom Water over much of global ocean abyss. These signatures represent changes in ventilation mediated by mixing and entrainment processes that may be location‐specific. Here we use available data to document, as best possible, those mixing processes as Weddell Sea Deep and Bottom Waters flow along the South Orkney Plateau, exit the Weddell Sea via Orkney Passage and fill the abyssal Scotia Sea. First, we find that an abrupt transition in topography upstream of Orkney Passage delimits the extent of the coldest waters along the Plateau's flanks and may indicate a region of especially intense mixing. Second, we revisit a control volume budget by Heywood et al. (2002) for waters trapped within the Scotia Sea after entering through Orkney Passage. This budget requires extremely vigorous water mass transformations with a diapycnal transfer coefficient of m2 s−1. Evidence for such intense diapycnal mixing is not found in the abyssal Scotia Sea interior and, while we do find large rates of diapycnal mixing in conjunction with a downwelling Ekman layer on the western side of Orkney Passage, it is insufficient to close the budget. This leads us to hypothesize that the Heywood budget is closed by a boundary mixing process in which the Ekman layer associated with the Weddell Sea Deep Water boundary current experiences relatively large vertical scale overturning associated with tidal forcing along the southern boundary of the Scotia Sea.

The interannual variability of potential temperature in the central Labrador Sea

The interannual variability of potential temperature in the central Labrador Sea is studied with a suite of numerical simulations with an eddy‐resolving regional ocean model and compared with available observations. The model successfully reproduces the observed variations in potential temperature at depths comprised between 150 and 2000 m over the period 1980–2009, capturing also the warming trend of the last decade and the deep water formation event in 2008. The suite of experiments allows for quantifying the contribution from the physical forcings responsible for the interannual variability of potential temperature in the region. The local atmospheric forcing drives the interannual signal by driving convection, while the incoming current system along the east coast of Greenland is responsible for about half of the warming trend (∼0.3–0.4°C) during the last decade through restratification process. The lateral transport of Irminger water in the convective region into the central Labrador Sea is further analyzed integrating a passive tracer. It is found that the overall amount of Irminger water transported in the convective region of the Labrador Sea is directly correlated with the amount of vertical convective mixing. In the last decade, following the decrease in convective activity, the model reveals a substantial decrease in concentration of Irminger Current water below 500 m in the Labrador Sea interior: by 2010 the overall amount is less than half than in the previous 20 years.

Structural geology and tectonics in marine science: Perspectives in the research of deep sea and deep interior

The fields of structural geology and tectonics have witnessed great progress over the last decade and are poised for further expansion in the future. One of the significant breakthroughs is the establishment of the ‘Beyond Plate Tectonics Theory’ where a combination of conceptual models and numerical modeling on plume tectonics and plate tectonics has enabled new insights into the structural and tectonic architecture and processes in the deep interior and deep sea. This paper synthesizes developments of structural geology and tectonics from a macroscopic perspective in deep interior and deep sea. Four key techniques are also reviewed: satellite altimetry for surface structures in deep-sea multi-beam sea-floor mapping; tomography for tectonics of the deep interior; diverse modeling approaches and software for unfolding dynamic evolution; and techniques for HT/HP experiments on material rheology and in situ component measurements.

Violent storms within the Sea: dense water formation episodes in the NW Mediterranean

Abstract. Heat and water exchanges in the ocean occur almost exclusively at the surface. As water compressibility is very low, stratification of the fluid is expected and horizontal motion is predominant in the sea interior. Among the few processes that may introduce a vertical component in the water motion are those that increase surface water density by freezing, cooling or evaporation. Those processes triggering convective motion are enhanced by cold surface air, dry wind and low solar radiation. Therefore, convective cells are more likely to occur when the temperature of the air at the sea surface is lower than sea surface temperature. Conversely, rain, river runoff, solar heating, calm and condensation at surface enhance stratification. Convective motion at sea has several scales ranging from few meters at the upper ocean, causing the surface mixed layer, to the entire water column, in what is known as deep convection. Only few places in the world ocean are suitable for deep convection, and only under particular weather conditions. In this paper, a brief review of the response to these particular conditions in the NW Mediterranean is presented in what is known as dense water formation. The violent sinking and spreading of water parcels that reach the deep sea floor in few hours is described. These are "hidden" mediterranean storms, occurring under the sea surface, "on the other side of the mirror".