Salinity Anomalies Research Articles

A new perspective of the 2014/15 failed El Ni\xf1o as seen from ocean salinity

This study investigates the 2014/15 failed El Niño using salinity from an ocean general circulation model. The results indicate that subsurface processes were especially strong in the summer of 2014 and they led to positive sea surface salinity anomalies in the central equatorial Pacific. The positive sea surface salinity anomalies induced a westward displacement of the sea surface salinity front that represents the eastern boundary of the western Pacific warm pool, preventing the warm surface water from shifting eastward as seen in a typical El Niño event. In the meantime, more salty water was transported equatorward by a strengthening subtropical cell in the South Pacific. The enhanced subsurface processes in the central equatorial Pacific conveyed the salinity anomalies of subtropical origin to the sea surface and were largely responsible for the sea surface salinity variability but had less impacts on sea surface temperature during the 2014/15 failed El Niño, suggesting some potential advantage of ocean salinity in the El Niño-Southern Oscillation prediction.

Detection of the 2012 Havre submarine eruption plume using Argo floats and its implications for ocean dynamics

More than 85% of the Earth's volcanism and geothermal heat release occurs underwater at mid-ocean ridges, intra-plate hotspots, and oceanic island arcs. However, we lack a clear understanding of how a submarine eruption interacts with the overlying water column, the structure of the submarine eruptive plume, and the transport of volcanic products in the ocean by these plumes. We describe here the detection of eruption-derived temperature increase and salinity decrease from the 2012 Havre submarine caldera eruption by an existing array of temperature/salinity profiling floats, known as Argo. The Argo floats observed the signal, significant at >3 sigma level with respect to the background ocean variability (noise), at ocean depths of ∼1750–2000 m deeper than the eruptive vent itself. In order to understand this signal, we develop a new conceptual submarine plume model which suggests that the sub-vent level temperature and salinity anomalies are caused by large-scale ocean mixing induced by the eruptive plume, rather than heating directly from the eruption. Using results from scaling analysis and a modified numerical plume-gravity current model, we show that submarine eruptions can efficiently advect water masses from the deep ocean closer to the surface and form multiple subsurface intrusions during the process. Consequently, the submarine eruptive plumes can initiate significant ocean mixing, a process with significant implications for both long- and short-term influence of submarine volcanism on ocean chemistry, dynamics, and ecology. Finally, our model confirms that a detectable anomaly would persist out to 100s of km from the eruption location, comparable to Argo's spatial sampling. Given the global ocean coverage and a decadal baseline, the Argo floats (and other similar datasets), in concert with hydrophone and seismic arrays, can provide significant new constraints on subaqueous volcanism, eruption dynamics, and the impact on Earth systems through enhanced ocean mixing and nutrient supply, e.g. during submarine Large Igneous Provinces.

The Mechanisms of the Atlantic Meridional Overturning Circulation Slowdown Induced by Arctic Sea Ice Decline

We explore the mechanisms by which Arctic sea ice decline affects the Atlantic meridional overturning circulation (AMOC) in a suite of numerical experiments perturbing the Arctic sea ice radiative budget within a fully coupled climate model. The imposed perturbations act to increase the amount of heat available to melt ice, leading to a rapid Arctic sea ice retreat within 5 years after the perturbations are activated. In response, the AMOC gradually weakens over the next ~100 years. The AMOC changes can be explained by the accumulation in the Arctic and subsequent downstream propagation to the North Atlantic of buoyancy anomalies controlled by temperature and salinity. Initially, during the first decade or so, the Arctic sea ice loss results in anomalous positive heat and salinity fluxes in the subpolar North Atlantic, inducing positive temperature and salinity anomalies over the regions of oceanic deep convection. At first, these anomalies largely compensate one another, leading to a minimal change in upper ocean density and deep convection in the North Atlantic. Over the following years, however, more anomalous warm water accumulates in the Arctic and spreads to the North Atlantic. At the same time, freshwater that accumulates from seasonal sea ice melting over most of the upper Arctic Ocean also spreads southward, reaching as far as south of Iceland. These warm and fresh anomalies reduce upper ocean density and suppress oceanic deep convection. The thermal and haline contributions to these buoyancy anomalies, and therefore to the AMOC slowdown during this period, are found to have similar magnitudes. We also find that the related changes in horizontal wind-driven circulation could potentially push freshwater away from the deep convection areas and hence strengthen the AMOC, but this effect is overwhelmed by mean advection.

Kuroshio intrusion into the South China Sea with an anticyclonic eddy: evidence from underwater glider observation

In this study, high-resolution temperature and salinity data obtained from three Sea-Wing underwater gliders were used together with satellite altimeter data to track the vertical thermohaline structure of an anticyclonic eddy that originated from the loop current of the Kuroshio southwest of Taiwan, China. One of the gliders crossed the entire eddy and it observed a remarkable warm anomaly of as much as 3.9°C extending to 500 dbar from the base of the mixed layer. Conversely, a positive salinity anomaly was found to be above 200 dbar only in the anticyclonic eddy, with a maximum value of >0.5 in the mixed layer. Below the mixed layer, water of higher salinity (>34.7) was found, which could have been preserved through constrained vertical mixing within the anticyclonic eddy. The salinity in the upper layer of the anticyclonic eddy was much similar to that of the northwestern Pacific Ocean than the northern South China Sea, reflecting Kuroshio intrusion with anticyclonic eddy shedding from the loop current.

The Ocean's Skin Layer in the Tropics.

We provide a large data set on salinity anomalies in the ocean's skin layer together with temperature anomalies and meteorological forcing. We observed an average salinity anomaly of 0.40 ± 0.41 practical salinity unity (n = 23,743), and in 83% of the observations the salinity anomaly was positive; that is, the skin layer was more saline. Temperature anomalies determined by an infrared camera were −0.23 ± 0.28 °C (upper 20‐μm layer in reference to nominal 1‐mm depth) and slightly warmer with −0.19 ± 0.25 °C in an upper 80‐μm layer in reference to 1‐m depth. In 75% of the observations, our data confirmed the presence of a cooler skin layer. Light rain rates (<4 mm/hr) induced an immediate freshening by 0.25 practical salinity unit in the skin layer without any effect in the mixed layer at 1‐m depth. Vertical mixing by strong winds (12 m/s) masked freshening during a heavy rain fall (47 mm/hr) by the intrusion of saltier deeper waters, but a freshening was observed after the wind and rain calmed down. We computed density anomalies, which suggest that denser skin layers can remain afloat up to a density anomaly of 1.3 g/L, likely due to the interfacial tension between the skin layer and underlying bulk water. It implies that salinization by evaporation regulates buoyancy fluxes, a key process for the exchange of climate‐relevant gases and heat between the ocean and atmosphere.

The nature of 60-year oscillations of the Arctic climate according to the data of the INM RAS climate model

Abstract Using the data of pre-industrial experiment with the INM-CM5 climate model for the period of 1200 years, we study the mechanism of natural oscillations of Arctic climate with the period of about 60 years. It is shown that for a quarter of the period prior to the Arctic warming there is a flow of Atlantic water into the Arctic ocean (AO) being more intense than usual, the salinity and density are less than usual near the coast and shelf border. As the result of advection of Atlantic water after Arctic warming, the water near the coast and shelf border becomes more salty and heavy, which leads to a weakening of the flow of Atlantic water and the change of oscillation phase. The conclusions are confirmed by calculations of the generation of anomalies of temperature, salinity, and velocity of currents by different terms, as well as estimation of the contribution of various components to the change of oscillation phase.

Effect of the Decadal Kuroshio Extension Variability on the Seasonal Changes of the Mixed‐Layer Salinity Anomalies in the Kuroshio‐Oyashio Confluence Region

AbstractThis study investigates the seasonal variations of the mixed‐layer salinity anomalies (MLSAs) under the decadal variability of the Kuroshio Extension (KE) in the Kuroshio‐Oyashio Confluence Region (KOCR: 35–40°N, 140–150°E). Our analysis reveals that the seasonal variation trend of the MLSA is almost opposite in the stable and unstable states of the KE. In the stable (unstable) state, the increasing (decreasing) MLSA in the KOCR reaches its maximal positive (minimal negative) value in late summer and then decreases (increases) gradually. An exploration of the budget of the MLSA shows that ocean dynamics explain more than half of the seasonal MLSA changes in the two states and exceed the contribution of atmospheric forcing (approximately 18%). The leading oceanic processes include advection of the mean mixed‐layer salinity by anomalous Ekman and geostrophic currents and advection of the MLSA by mean geostrophic currents, which explain 13.80%, 12.90%, and 20.73% (11.59%, 13.36%, and 24.90%) of the MLSA temporal changes in the stable (unstable) states, respectively. The difference in the MLSA between the two states is primarily derived from the discrepancies in the anomalous ocean currents in the KOCR and south of Japan, salinity anomalies in the south of Japan, and sea surface temperature anomalies affecting atmospheric forcing between the two modes of the KE. Moreover, the most apparent influences are concentrated in summer and early autumn because of the shallower mixed layer in terms of atmospheric forcing and obvious velocity changes and the distribution of climatological salinity for ocean processes.

An Observational Perspective of Sea Surface Salinity in the Southwestern Indian Ocean and Its Role in the South Asia Summer Monsoon

The seasonal variability of sea surface salinity anomalies (SSSAs) in the Indian Ocean is investigated for its role in the South Asian Summer Monsoon. We have observed an elongated spatial-feature of the positive SSSAs in the southwestern Indian Ocean before the onset of the South Asian Summer Monsoon (SASM) by using both the Aquarius satellite and the Argo float datasets. The maximum variable areas of SSSAs in the Indian Ocean are along (60 ° E–80 ° E) and symmetrical to the equator, divided into the southern and northern parts. Further, we have found that the annual variability of SSSAs changes earlier than that of sea surface temperature anomalies (SSTAs) in the corresponding areas, due to the change of wind stress and freshwater flux. The change of barrier layer thickness (BLT) anomalies is in phase with that of SSSAs in the southwestern Indian Ocean, which helps to sustain the warming water by prohibiting upwelling. Due to the time delay of SSSAs change between the northern and southern parts, SSSAs, therefore, take part in the seasonal process of the SASM via promoting the SSTAs gradient for the cross-equator currents.

Annual and Interannual Variability in the California Current System: Comparison of an Ocean State Estimate with a Network of Underwater Gliders

AbstractA data-constrained state estimate of the southern California Current System (CCS) is presented and compared with withheld California Cooperative Oceanic Fisheries Investigations (CalCOFI) data and assimilated glider data over 2007–17. The objective of this comparison is to assess the ability of the California State Estimate (CASE) to reproduce the key physical features of the CCS mean state, annual cycles, and interannual variability along the three sections of the California Underwater Glider Network (CUGN). The assessment focuses on several oceanic metrics deemed most important for characterizing physical variability in the CCS: 50-m potential temperature, 80-m salinity, and 26 kg m−3 isopycnal depth and salinity. In the time mean, the CASE reproduces large-scale thermohaline and circulation structures, including observed temperature gradients, shoaling isopycnals, and the locations and magnitudes of the equatorward California Current and poleward California Undercurrent. With respect to the annual cycle, the CASE captures the phase and, to a lesser extent, the magnitude of upper-ocean warming and stratification from late summer to early fall and of isopycnal heave during springtime upwelling. The CASE also realistically captures near-surface diapycnal mixing during upwelling season and the semiannual cycle of the California Undercurrent. In terms of interannual variability, the most pronounced signals are the persistent warming and downwelling anomalies of 2014–16 and a positive isopycnal salinity anomaly that peaked with the 2015–16 El Niño.

Potential Predictability of Multidecadal Oscillations of Sea Surface Temperature in the Arctic and Their Sensitivity to External Forcings

The low-frequency variability of sea surface temperature and salinity in the Arctic is analyzed using the data of the 1200-year preindustrial experiment with the INM-CM5 climate model developed in the Marchuk Institute of Numerical Mathematics of Russian Academy of Sciences. It is shown that the leading variability pattern is a regular coupled oscillation of temperature and salinity with the period of about 50 years. The empirical method based on the fluctuation-dissipation theorem was applied to evaluate influence functions which provide the optimum excitation of this oscillation phases. It is demonstrated that salinity anomalies are the main driver of this variability. The time of potential predictability of sea surface temperature and salinity was determined using the analog method, it equals about six years for 15-year means. The main source of long-term predictability is the spatial pattern associated with the leading mode of low-frequency variability of the analyzed parameters in the Arctic.

Rapid warming and salinity changes in the Gulf of Maine alter surface ocean carbonate parameters and hide ocean acidification

A profound warming event in the Gulf of Maine during the last decade has caused sea surface temperatures to rise to levels exceeding any earlier observations recorded in the region over the last 150 years. This event dramatically affected CO2 solubility and, in turn, the status of the sea surface carbonate system. When combined with the concomitant increase in sea surface salinity and assumed rapid equilibration of carbon dioxide across the air sea interface, thermodynamic forcing partially mitigated the effects of ocean acidification for pH, while raising the saturation index of aragonite (varOmega_{AR}) by an average of 0.14 U. Although the recent event is categorically extreme, we find that carbonate system parameters also respond to interannual and decadal variability in temperature and salinity, and that such phenomena can mask the expression of ocean acidification caused by increasing atmospheric carbon dioxide. An analysis of a 34-year salinity and SST time series (1981–2014) shows instances of 5–10 years anomalies in temperature and salinity that perturb the carbonate system to an extent greater than that expected from ocean acidification. Because such conditions are not uncommon in our time series, it is critical to understand processes controlling the carbonate system and how ecosystems with calcifying organisms respond to its rapidly changing conditions. It is also imperative that regional and global models used to estimate carbonate system trends carefully resolve variations in the physical processes that control CO2 concentrations in the surface ocean on timescales from episodic events to decades and longer.

Mediterranean Sea climatic indices: monitoring long-term variability and climate changes

Abstract. We present a new product composed of a set of thermohaline climatic indices from 1950 to 2015 for the Mediterranean Sea such as decadal temperature and salinity anomalies, their mean values over selected depths, decadal ocean heat and salt content anomalies at selected depth layers as well as their long time series. It is produced from a new high-resolution climatology of temperature and salinity on a 1∕8∘ regular grid based on historical high-quality in situ observations. Ocean heat and salt content differences between 1980–2015 and 1950–1979 are compared for evaluation of the climate shift in the Mediterranean Sea. The two successive periods are chosen according to the standard WMO climate normals. The spatial patterns of heat and salt content shifts demonstrate that the climate changes differently in the several regions of the basin. Long time series of heat and salt content for the period 1950 to 2015 are also provided which indicate that in the Mediterranean Sea there is a net mean volume warming and salinification since 1950 that has accelerated during the last two decades. The time series also show that the ocean heat content seems to fluctuate on a cycle of about 40 years and seems to follow the Atlantic Multidecadal Oscillation climate cycle, indicating that the natural large-scale atmospheric variability could be superimposed onto the warming trend. This product is an observation-based estimation of the Mediterranean climatic indices. It relies solely on spatially interpolated data produced from in situ observations averaged over decades in order to smooth the decadal variability and reveal the long-term trends. It can provide a valuable contribution to the modellers' community, next to the satellite-based products, and serve as a baseline for the evaluation of climate-change model simulations, thus contributing to a better understanding of the complex response of the Mediterranean Sea to the ongoing global climate change. The product is available in netCDF at the following sources: annual and seasonal T∕S anomalies (https://doi.org/10.5281/zenodo.1408832), annual and seasonal T∕S vertical averaged anomalies (https://doi.org/10.5281/zenodo.1408929), annual and seasonal areal density of OHC/OSC anomalies (https://doi.org/10.5281/zenodo.1408877), annual and seasonal linear trends of T∕S, OHC/OSC anomalies (https://doi.org/10.5281/zenodo.1408917), annual and seasonal time series of T∕S, OHC/OSC anomalies (https://doi.org/10.5281/zenodo.1411398), and differences of two 30-year averages of annual and seasonal T∕S, OHC/OSC anomalies (https://doi.org/10.5281/zenodo.1408903).

Satellite detection of an unusual intrusion of salty slope water into a marginal sea: Using SMAP to monitor Gulf of Maine inflows

Satellite salinity from the Soil Moisture Active Passive (SMAP) mission and in situ observations are used to diagnose the source of a significant increase in warm and salty surface water entering the Gulf of Maine (GoM) in the winter of 2017–2018. SMAP salinity anomaly data indicate that this event was related to a salty feature that moved along the northwestern Atlantic shelf break from near the Grand Banks southwest towards the GoM over eight months before entering the Gulf in December 2017 to January 2018. Satellite altimetry, sea surface salinity, and sea surface temperature data suggest that, before entering the GoM, the salty feature interacted with Gulf Stream meanders and eddies several times, helping to sustain the water mass. It is likely that feature interactions with a warm Gulf Stream meander took place in the fall of 2017, helping to advect high salinity water onto the shelf and then into the GoM as a surface trapped feature in late fall 2017. According to satellite salinity data, this episode led to significant salinification (about 1 psu) in the northeastern GoM. Interior GoM buoy salinity data agree in showing four months of increased GoM salinity of the upper 50 m starting in November 2017. Buoy T/S analyses characterize this surface inflow as modified warm Atlantic slope water, typically seen only below 100 m and previously unobserved at the surface in the 15-year buoy record. This new salty water circulated cyclonically along the GoM coastline and mixed into the deeper Gulf through February 2018. Its intrusion may have also enhanced the cyclonic winter circulation in the Gulf. GoM surface salinity anomalies ended abruptly in early March 2018 coincident with the occurrence of a bomb cyclone and its associated strong upper ocean mixing.

Field-observation for an anticyclonic mesoscale eddy consisted of twelve gliders and sixty-two expendable probes in the northern South China Sea during summer 2017

An intensive field observation experiment using 12 Chinese gliders equipped with conductivity-temperature-depth (CTD) sensors and 62 expendable CTD probes (XCTDs) was performed to investigate the 3-D structure and time evolution of an anticyclonic eddy in the northern South China Sea (NSCS). The observed results showed that the anticyclonic eddy had a horizontal radius of about 80 km at surface and a vertical depth of impact of more than 1000 m. The largest temperature and salinity anomalies compared with the averaged values of the temperature and salinity profiles were 3.5°C and 0.4 psu at 120 m depth, respectively. Combined analysis of altimeter sea level and water mass properties indicated that the anticyclonic eddy was shed from the Kuroshio loop current. The vertical axis of the anticyclonic eddy tilted from surface to the observed maximum depth (1000 m) along its translation direction against the 2000 m isobath. The center of the anticyclonic eddy remained in the region east of Dongsha Island for more than half a month. During this time, the long axis direction of the eddy changed from across the slope to along the slope. Then, the eddy moved southward along the 2000 m isobaths. Both the geostrophic current and temperature distribution revealed that the eddy intensity weakened during the observation period gradually. These observations indicated strong interaction between the anticyclonic eddy and the slope topography of Dongsha Island.

Spiciness Anomalies in the Upper South Indian Ocean

AbstractThis study investigates an isopycnal temperature/salinity T/S, or spiciness, anomaly in the upper south Indian Ocean for the period from 2004 to 2015 using observations and reanalyses. Spiciness anomalies at about 15°S on 24–26σθ are focused on, whose standard deviation is about 0.1 psu in salinity and 0.25°C in temperature, and they have a contribution to isobaric temperature variability comparable to thermocline heave. A plausible generation region of these anomalies is the southeastern Indian Ocean, where the 25σθ surface outcrops in southern winter, and the anticyclonic subtropical gyre advects subducted water equatorward. Unlike the Pacific and Atlantic, spiciness anomalies in the upper south Indian Ocean are not T/S changes in mode water, and meridional variations in SST and sea surface salinity in their generation region are not density compensating. It is possible that this peculiarity is owing to freshwater originating from the Indonesian Seas. The production of spiciness anomalies is estimated from surface heat and freshwater fluxes and the surface T/S relationship in the outcrop region, based on several assumptions including the dominance of surface fluxes in the surface T/S budget and effective mixed layer depth proposed by Deser et al. The result agrees well with isopycnal salinity anomalies at the outcrop line, which indicates that spiciness anomalies are generated by local surface fluxes. It is suggested that the Ningaloo Niño and El Niño–Southern Oscillation lead to interannual variability in surface heat flux in the southeastern Indian Ocean and contribute to the generation of spiciness anomalies.

Composite eddy structures on both sides of the Luzon Strait and influence factors

Combining Argo observations with satellite remote sensing data during the period of 2002–2014, the mean three-dimensional structures of mesoscale eddies on both sides of the Luzon Strait (LS) were obtained via a composite method and analyzed to statistically examine the influences of background marine environment and the Kuroshio current on the eddy structures. The significant signals of temperature and salinity anomalies within the composite eddies extend much deeper in the region east of the LS (zone E) than those in the region west of the strait (zone W) because of stronger eddy intensity and larger vertical gradients of background temperature and salinity in the deep layer in zone E. In the vertical structure of temperature anomaly within the eddies, two cores occur at around 200 and 400 dbar depths, respectively, in zone E and only one core is centered at about 100 dbar in zone W. There is a clear three-core sandwich pattern in the vertical structure of salinity anomaly within the eddies in zone E. The Kuroshio water trapped in the eddy is responsible for abnormally positive salinity anomaly in the surface layer of the anticyclonic eddy center in zone W. On both sides of the LS, an asymmetric dipole structure in the surface layer gradually turns into a monopole one at depths, which resulted from the competition between horizontal advection effect and eddy pumping effect. The Kuroshio current influences the distribution patterns of isotherms and isohalines and enhances background temperature and salinity horizontal gradients on both sides of the LS, determining the orientations of dipole temperature and salinity structures within eddies.

SIDDIES Corridor: A Major East‐West Pathway of Long‐Lived Surface and Subsurface Eddies Crossing the Subtropical South Indian Ocean

AbstractSouth Indian Ocean eddies (SIDDIES), originating from a high evaporation region in the eastern Indian Ocean, are investigated by tracking individual eddies from satellite data and co‐located Argo floats. A subsurface‐eddy identification method, based on its steric dynamic height anomaly, is devised to assign Argo profiles to surface eddies (surfSIDDIES) or subsurface eddies (subSIDDIES). These westward‐propagating, long‐lived features (&gt;3 months) prevail over a preferential latitudinal band, forming a permanent structure linking the eastern to the western Indian Ocean, that we call the 'SIDDIES Corridor’. Key features have been revealed in the mean thermohaline vertical structure of these eddies. Anticyclonic SIDDIES are characterized by positive subsurface salinity anomalies, with subSIDDIES not exhibiting negative surface anomalies, as opposed to surfSIDDIES. Cyclonic subSIDDIES also occur, but their related salinity anomalies are weaker. SubSIDDIES exhibit two cores of different temperature polarities in their surface and subsurface levels. Cyclonic subSIDDIES have their cores at around 150‐200 m depth along the 25.4‐25.8 kg m−3 potential density layer with anticyclonic subSIDDIES having their cores at 250‐300 m along the 26‐26.4 kg m−3 density layer. The SIDDIES corridor acts as a zonal pathway for both eddy‐types to advect water masses and biogeochemical properties across the basin. This study provides a new insight on heat/salt fluxes, showing that 58% (32%) of the total heat eddy‐flux is ascribed to cyclonic (anticyclonic) subSIDDIES, respectively, in the eastern South Indian Ocean. Anticyclonic subSIDDIES have also been found to be the sole high‐saline water eddy‐conveyor toward the western Indian Ocean.

Thermohaline structure, transport and evolution of the Black Sea eddies from hydrological and satellite data

Combination of altimetry-based method of eddy identification and historical hydrological measurements for 1992–2015 is used to analyze the thermohaline and dynamic structure of the Black Sea eddies and its relation with eddy intensity, eddy age and season of a year. Anticyclonic eddies (AEs) are characterized by negative salinity anomalies, which can reach −1.7 psu at the depth of the main halocline. The temperature anomalies are positive in their upper layers, and negative in the deeper layers, because of the vertical displacement of the waters of the Cold Intermediate Layer (CIL). Cyclonic eddies (CEs) have the opposite structure with increased salinity, colder upper layers and warmer deeper layers. Thermohaline anomalies in the eddies of both signs are maximal in summer, while in winter they are shallowest and minimal. The displacement of pycnocline in eddies causes the decrease/increase of stratification in the upper layer of AEs/CEs and opposite increase/decrease in their deeper layers. It also causes the deepening/uplift of the layer of maximum geostrophic vertical shear in AEs/CEs. The latter is the probable reason of the observed higher intensity and deeper penetration of orbital velocities in AEs than in CEs. The changes of isopycnals positions during the eddies’ lifetime are used to quantify the evolution of vertical velocity in AEs and CEs. In the beginning of AEs life during intensification phase, vertical velocity is directed downward, while during the decaying phase it change its sign and is directed upward. The opposite is observed in CEs. Vertical velocity is maximal at the pycnocline depth of 100–110 m with values changing from (−8 to 8) ∗ 10−6 m/s in AEs, and from (+5 to −25) ∗ 10−6 m/s in CEs. Eddies thermohaline structure and altimetry-derived orbital velocity is tightly related. This relation obtained in the study and altimetry-derived data on the distribution of eddy frequency, translational speed and orbital velocity is used to quantify eddies salt, heat content and transport in the basin. The transport velocity of water in the eddies core (2–4 cm/s) is significantly smaller than the average velocity of the large-scale currents (∼10–40 cm/s). Such slowing causes the “relative” transport of eddies against the mean flow direction. This effect leads to the accumulation of brackish and cold water in the deep layers of east Black Sea and maintain the observed east-west asymmetry of the basin thermohaline fields.

Ocean Impacts on Australian Interannual to Decadal Precipitation Variability

In Australia, successful seasonal predictions of wet and dry conditions are achieved by utilizing the remote impact of sea surface temperature (SST) variability in tropical oceans, particularly the Pacific Ocean, on the seasonal timescale. Beyond seasonal timescales, however, it is still unclear which processes and oceans contribute to interannual-to-decadal wet/dry conditions in Australia. This research examines the interannual-to-decadal relationship between global SST anomalies (SSTAs) and Australian wet/dry variability by analyzing observational data and global climate model experiments conducted with the NCAR Community Earth System Model (CESM) and the Model for Interdisciplinary Research on Climate (MIROC). A 10-member ensemble simulation suite for 1960–2015 (CESM) and 1950–2010 (MIROC) is conducted by assimilating the observed three-dimensional ocean temperature and salinity anomalies into fully coupled global climate models. In both observational analyses and ocean assimilation experiments, the most dominant annual mean precipitation variability shows a clear relationship with SSTAs in the tropical Pacific and the Atlantic. Our partial ocean assimilation experiment, in which the ocean component of the CESM and MIROC are assimilated by the observed ocean temperature and salinity anomalies in the equatorial Pacific only, shows that the tropical Pacific SST variability is the main driver of Australian precipitation variability on the interannual-to-decadal timescales. However, our additional partial ocean assimilation experiment, in which the climate models incorporate the observed anomalies solely in the Atlantic ocean, demonstrates that the Atlantic Ocean can also affect Australian precipitation variability on the interannual-to-decadal timescale through changes in tropical Pacific SSTAs and the modulation of the global Walker circulation. Our results suggest that about a half of Australian interannual-to-decadal precipitation variability originates from the Atlantic Ocean.

A New Assessment of Mesoscale Eddies in the South China Sea: Surface Features, Three‐Dimensional Structures, and Thermohaline Transports

AbstractBy analyzing 22 years (1993–2015) of daily eddy data, statistics of surface eddy properties were refreshed in the South China Sea. More than 7,000 of historical Argo profiles were collocated into eddy‐centered coordinates to reveal the composite mean three‐dimensional structure of eddies. The results indicate that eddies of both polarities have long conical shape, with a maximum (minimum) density anomaly of 0.55 kg/m3 (−0.51 kg/m3) at 60 m (90 m) in the composite cyclonic (anticyclonic) eddy. Temperature and salinity anomalies also peak at eddy cores, with values of −1.5 °C and 0.15 psu in the cyclonic eddy and 1.4 °C and −0.16 psu in the anticyclonic eddy. The temperature and density anomalies extend vertically to 400–500 m, while the salinity anomalies are apparent only in the upper 150 m. The temperature anomalies contribute about 90% of the density anomalies. Mixed layer depths in cyclonic eddies are on average 15 m shallower than those in anticyclonic eddies. The rotation of the composite cyclonic (anticyclonic) eddy generates meridional heat transport of 1.4 × 1012 W (−3.1 × 1012 W) and salt transport of −4.0 × 104 kg/s (5.6 × 104 kg/s). More than 90% of the heat and salt transports are concentrated in the upper 300 and 100 m, respectively. Compared to the meridional transports, the westward propagation of eddies results in zonal heat and salt transports on the same orders of magnitudes. The westward propagation of eddies also generates a basin‐scale westward water transport of 1.4 Sv, equivalent to about 30% of the annual‐mean Luzon Strait transport.