Changes In Surface Salinity Research Articles

Surface Salinity Changes of the Tropical and Subtropical Oceans Since 1970 and Their Relationship With Surface Freshwater Fluxes

AbstractSea surface salinity (SSS) has shown a broad‐scale trend pattern of “salty gets saltier, fresh gets fresher” during the past decades, in line with changes in surface freshwater fluxes (FWFs). Yet, regional SSS changes and their relationship with FWFs are more complex and less appreciated, causing uncertainties in understanding the link between ocean salinity and the global water cycle. Based on the Hybrid Coordinate Ocean Model, we simulated the observed trends of tropical freshening and subtropical salinification since 1970 and gained insight into underlying processes through sensitivity experiments. Albeit with regional differences, changes in precipitation rate are the leading driver for SSS trends in most parts of the tropical and subtropical oceans, with a contribution of typically >60% in six selected regions. The roles of wind‐driven ocean dynamics and evaporation are secondary, contributing by <20% and <30%, respectively. Our results also suggest notable regional contrasts in the SSS‐FWF relationship. Particularly, many regions within the 10°–20° bands show opposite trends in SSS and FWF. Both the climatological and perturbed circulations are essential in this regionality. Specifically, the poleward Ekman transports driven by tropical trade winds act to broaden the SSS‐freshening regions generated by increased tropical rainfall; wind‐driven alterations in the geostrophic circulation cause SSS advection across zonal salinity gradients. These processes drive SSS changes that are opposite in sign to local FWF changes and complicate the regional SSS‐FWF relationship in the long‐term change since 1970.

Estimation of subsurface salinity and analysis of Changjiang diluted water volume in the East China Sea

In the East China Sea (ECS), the sea surface salinity (SSS) changes as the Changjiang Diluted Water (CDW) propagates toward the Korean Peninsula via the ocean current and winds every summer annually. Although the vertical stratifications resulting from the CDW volume changes are important, it has not been analyzed yet. Therefore, in this study, we aimed to estimate the salinity at a depth of 10 m (S10m) using convolutional neural network (CNN) model based on multi-satellite measurements and analyze CDW volume variations. The main CDW mass in the ECS reaches approximately 10 m in depth; thus, the CNN model was developed using sea surface physical factors as input and in situ S10m obtained from the National Institute of Fisheries Science (NIFS) as ground truth data from 2015 to 2021. The CNN tests result showed a determination coefficient (R2) of 0.81, root mean square error (RMSE) of 0.63 psu, and relative RMSE (RRMSE) of 2.00%. Unlike the sea surface distribution, the spatial distribution of S10m showed that the CDW was predominantly present in the center of the ECS. From SHapley Additive exPlanations (SHAP) analysis, SSS exhibited a strong positive relationship with S10m, and the sea level anomaly showed a strong negative relationship. After calculating the volume of the CDW from the surface to a depth of 10 m, the maximum (3.01×1012 m3) and minimum volumes (1.31×1012 m3) were represented in 2016 and 2018, respectively. Finally, the warming effect induced by the CDW volume changes was analyzed in two different years: 2016 and 2018. Specifically, in 2016, the sea surface temperature increased by more than 4.79 °C in the Ieodo location, while in 2018, it increased by 2.19 °C. Thus, our findings can obtain information about the volume variation of the CDW and its effect on the ECS in summer.

Disentangling the impact of Atlantic Niño on sea-air CO2 flux

Atlantic Niño is a major tropical interannual climate variability mode of the sea surface temperature (SST) that occurs during boreal summer and shares many similarities with the tropical Pacific El Niño. Although the tropical Atlantic is an important source of CO2 to the atmosphere, the impact of Atlantic Niño on the sea-air CO2 exchange is not well understood. Here we show that the Atlantic Niño enhances (weakens) CO2 outgassing in the central (western) tropical Atlantic. In the western basin, freshwater-induced changes in surface salinity, which considerably modulate the surface ocean CO2 partial pressure (pCO2), are the primary driver for the observed CO2 flux variations. In contrast, pCO2 anomalies in the central basin are dominated by the SST-driven solubility change. This multi-variable mechanism for pCO2 anomaly differs remarkably from the Pacific where the response is predominantly controlled by upwelling-induced dissolved inorganic carbon anomalies. The contrasting behavior is characterized by the high CO2 buffering capacity in the Atlantic, where the subsurface water mass contains higher alkalinity than in the Pacific.

Eddy-induced sea surface salinity changes in the South China Sea

Eddy-induced sea surface salinity (SSS) changes are systematically studied in the South China Sea (SCS) by using Soil Moisture Active Passive (SMAP) satellite salinity data from 2015 to 2021 for the first time. All eddies in the SCS during this period are analysed, and two normalized eddy composites are reconstructed under the long-term basin mean. In general, anticyclonic eddies (AEs) tend to result in lower salinity than cyclonic eddies (CEs) in the upper ocean. The salinity anomalies of the AE and CE composites are dominated by dipole and monopole structures, respectively. The different patterns in eddy-induced salinity anomalies are generally controlled by horizontal and vertical advections, which is further confirmed by their seasonal evolutions. A spatiotemporal decomposition of these salinity anomaly patterns suggests that the dipole and monopole patterns account for more than 70% of the salinity variability. All the eddies in the SCS are monopole-dominated and dipole-supplemented overall. This finding infers a relatively uniform eddy-induced salinity structure across the SCS and provides an observational-based metric for future model studies.

Attribution of the Subsurface Temperature Change in the Southern Hemisphere

Abstract The Southern Hemisphere temperature has experienced obvious changes with great spatial differences over the past several decades. Most regions show extreme warming, especially those located at 35°–55°S. In contrast, subsurface cooling exists between 15° and 35°S in the Indian and Pacific basins. The subsurface temperature and salinity change can be divided into spiciness change and heave components. The results show the warming due to isopycnal movement being largely offset by significant spiciness cooling at middepth. Surface warming and subduction into the interior ocean account for subsurface spiciness cooling near 45°S, while surface freshening and penetration along isopycnals are more important to the subsurface spiciness cooling farther north. The isobaric temperature change is associated with pure warming and pure heaving, and the subsurface cooling observed in the Indian and Pacific subtropics is predominantly attributed to pure heaving. This study provides a quantitative estimate of the relative contribution of surface temperature, salinity change, and circulation adjustment in subsurface temperature change, highlighting the importance of circulation change in producing subsurface cooling. Further research is needed to understand why different processes dominate in different ocean sections. Significance Statement While the global ocean is warming, the subsurface temperature change exhibits a significant regional disparity. This paper attempts to explain the deep-reaching warming at 35°–55°S and cooling at 15°–35°S based on three historical observation datasets. We find that the cooling mostly occurs between 400 and 1000 m in the south Indian and Pacific subtropics (15°–35°S), which is attributed to pure heaving, indicating the importance of circulation change in these regions. The midlatitude warming (35°–55°S) is mainly caused by the pure warming process, which is related to heat uptake at the subpolar surface and northward and downward heat transport. The spiciness cooling near 45°S is mainly driven by the subduction of the surface warming signal while the freshening process has a stronger impact on spiciness cooling farther north.

Sea Surface Salinity Changes in Response to El Niño–like SST Warming and Relevant Ocean Dynamics in the Tropical Pacific under the CMIP6 Abrupt-4XCO2 Scenario

Abstract Based on the abrupt-4XCO2 scenario in phase 6 of the Coupled Model Intercomparison Project (CMIP6), this study investigates the response of the rainfall changes to El Niño–like SST warming and the role of ocean dynamical processes in the salinity changes in the tropical Pacific. The results show that the Walker circulation weakening and eastward shift, related to El Niño–like SST warming, dominates the zonal precipitation change. Precipitation decreases (increases) in the Maritime Continent (the equatorial Pacific), partly offsetting the effect of specific humidity. At the same time, the El Niño–like warming triggers convergence of meridional winds, which leads to a precipitation increase in the equatorial Pacific and a decrease in the intertropical convergence zone and the South Pacific convergence zone, following the “warmer-get-wetter” mechanism. Unlike the spatial pattern of precipitation changes, the sea surface salinity changes become fresher in the tropical western Pacific, related to the precipitation and the mean horizontal advection. The precipitation increase leads to negative salinity anomalies in the equatorial central Pacific. The westward climatological zonal currents transport the negative salinity anomalies westward. The meridional currents advect the salinity anomalies to both sides of the equator, partly offsetting the contribution of the freshwater flux on the salinity change. In addition, shallower mixed layer depth and weakening upwelling bring less high-salinity water to the surface and impact salinity redistribution through the vertical process in the equatorial regions.

Research on the insurance of swimming crab temperature and salinity index insurance based on Copula function.

Under climate change, the sea surface temperature and salinity change greatly, which poses a considerable threat to sustainable food security. Sea surface temperature and salinity (SST/SSS) are selected to examine the annual output of swimming crab in 24 cities along the eastern China. The Copula-based function was used to construct the probability distribution model of the swimming crab yield with SST and SSS. The pure premium rate of the swimming crab production in these 24 cities are also examined. The results show that 1) There is significant positive correlations between the yield of swimming crab with temperature and salinity over the study area. The only exception is that the correlation between yield of swimming crab and salinity is not significant in the south of study area. 2) The span of the pure insurance premium rate of swimming crab in 24 cities increases rapidly with the increase of the protection level, the maximum span up to 2.04%, and the minimum span is only 1.6%. 3) The distribution of the swimming crab insurance premium rate is various in space. The insurance premium rate of 8 cities in the south of Taizhou is low with the highest premium rate at 5.6%. The insurance premium rate of 16 cities in north of Taizhou is relatively high with the rate between 6%-22%. The research can provide a theoretical basis for the pricing of insurance products for swimming crab in 24 cities in the typical aquaculture areas in eastern China.

Ocean Surface Salinity Response to Atmospheric River Precipitation in the California Current System

Abstract Atmospheric rivers (ARs) result in precipitation over land and ocean. Rainfall on the ocean can generate a buoyant layer of freshwater that impacts exchanges between the surface and the mixed layer. These “fresh lenses” are important for weather and climate because they may impact the ocean stratification at all time scales. Here we use in situ ocean data, collocated with AR events, and a one-dimensional configuration of a general circulation model, to investigate the impact of AR precipitation on surface ocean salinity in the California Current System (CCS) on seasonal and event-based time scales. We find that at coastal and onshore locations the CCS freshens through the rainy season due to AR events, and years with higher AR activity are associated with a stronger freshening signal. On shorter time scales, model simulations suggest that events characteristic of CCS ARs can produce salinity changes that are detectable by ocean instruments (≥0.01 psu). Here, the surface salinity change depends linearly on rain rate and inversely on wind speed. Higher wind speeds (U > 8 m s−1) induce mixing, distributing freshwater inputs to depths greater than 20 m. Lower wind speeds (U ≤ 8 m s−1) allow freshwater lenses to remain at the surface. Results suggest that local precipitation is important in setting the freshwater seasonal cycle of the CCS and that the formation of freshwater lenses should be considered for identifying impacts of atmospheric variability on the upper ocean in the CCS on weather event time scales. Significance Statement Atmospheric rivers produce large amounts of rainfall. The purpose of this study is to understand how this rain impacts the surface ocean in the California Current System on seasonal and event time scales. Our results show that a greater precipitation over the rainy season leads to a larger decrease in salinity over time. On shorter time scales, these atmospheric river precipitation events commonly produce a surface salinity response that is detectable by ocean instruments. This salinity response depends on the amount of rainfall and the wind speed. In general, higher wind speeds will cause the freshwater input from rain to mix deeper, while lower wind speeds will have reduced mixing, allowing a layer of freshwater to persist at the surface.

Sea surface salinity changes and trans-basin water vapor transport between the Atlantic and Pacific under CMIP6 abrupt-4xCO2 scenario

Sea surface salinity changes and trans-basin water vapor transport between the Atlantic and Pacific under CMIP6 abrupt-4xCO2 scenario

Surface warming-induced global acceleration of upper ocean currents.

How the ocean circulation changes in a warming climate is an important but poorly understood problem. Using a global ocean model, we decompose the problem into distinct responses to changes in sea surface temperature, salinity, and wind. Our results show that the surface warming effect, a robust feature of anthropogenic climate change, dominates and accelerates the upper ocean currents in 77% of the global ocean. Specifically, the increased vertical stratification intensifies the upper subtropical gyres and equatorial currents by shoaling these systems, while the differential warming between the Southern Ocean upwelling zone and the region to the north accelerates surface zonal currents in the Southern Ocean. In comparison, the wind stress and surface salinity changes affect regional current systems. Our study points a way forward for investigating ocean circulation change and evaluating the uncertainty.

A case study of paleoenvironmental interactions during the Miocene Climate Optimum in southwestern Paratethys

The marine system of the Mediterranean-Paratethys region in the Middle Miocene was influenced by the global climatic changes corresponding to the Miocene Climate Optimum. The latter was characterized by global warming of deep oceanic waters succeeded by a decrease of wind activity and ocean water circulation together with a decline in oceanic productivity. This study provides a detailed paleoenvironmental and depositional history of the Middle Miocene deposits from Mt. Požeška Gora (the east part of Croatia). Stable carbon and oxygen isotope data with foraminiferal fauna coupled together with palynological data indicate both seasonal and long-term changes in surface water temperatures, nutrient contents, and salinity. Furthermore, it was possible to determine two phases of Middle Miocene flooding in the studied marine system: (a) a shallow, high nutrient marginal sea strongly affected by freshwater inputs corresponding to the thermal maximum and periods with enhanced precipitation during the Miocene Climate Optimum, and (b) a younger deeper marginal sea with a developed seasonal stratification, rather intermediate nutrient availability and reduced fresh-water inputs. Based on the microbiostratigraphy and strontium isotope stratigraphy (87Sr/86Sr) coupled with previously published high-precision geochronology, the timing of the first and second flooding can be correlated with the Langhian age - ≤15.4 Ma and 14.6 Ma, respectively Possibly, the properties of the surficial waters that were described as a part of the flooding phases in individual time intervals can indicate changes in circulation patterns as a result of potential influence of the open-sea water masses.

The contribution of melt ponds to enhanced Arctic sea-ice melt during the Last Interglacial

Abstract. The Hadley Centre Global Environment Model version 3 (HadGEM3) is the first coupled climate model to simulate an ice-free Arctic during the Last Interglacial (LIG), 127 000 years ago. This simulation appears to yield accurate Arctic surface temperatures during the summer season. Here, we investigate the causes and impacts of this extreme simulated ice loss. We find that the summer ice melt was predominantly driven by thermodynamic processes: atmospheric and ocean circulation changes did not significantly contribute to the ice loss. We demonstrate these thermodynamic processes were significantly impacted by melt ponds, which formed on average 8 d earlier during the LIG than during the pre-industrial control (PI) simulation. This relatively small difference significantly changed the LIG surface energy balance and impacted the albedo feedback. Compared to the PI simulation: in mid-June, of the absorbed flux at the surface over ice-covered cells (sea-ice concentration > 0.15), ponds accounted for 45 %–50 %, open water 35 %–45 %, and bare ice and snow 5 %–10 %. We show that the simulated ice loss led to large Arctic sea surface salinity and temperature changes. The sea surface temperature and salinity signals we identify here provide a means to verify, in marine observations, if and when an ice-free Arctic occurred during the LIG. Strong LIG correlations between spring melt pond and summer ice area indicate that, as Arctic ice continues to thin in future, the spring melt pond area will likely become an increasingly reliable predictor of the September sea-ice area. Finally, we note that models with explicitly modelled melt ponds seem to simulate particularly low LIG sea-ice area. These results show that models with explicit (as opposed to parameterised) melt ponds can simulate very different sea-ice behaviour under forcings other than the present day. This is of concern for future projections of sea-ice loss.

Decadal changes in size, salinity, waterbirds, and fish in lakes of the Konya Closed Basin, Turkey, associated with climate change and increasing water abstraction for agriculture

ABSTRACT The Konya Closed Basin (KCB) in Turkey has a cold semiarid to warm Mediterranean climate and hosts the largest Turkish freshwater lake, Lake Beyşehir, and the iconic saline Lake Tuz. Using published as well as our own ground-truth and remote sensing data, we provide (1) a brief description of the paleoenvironmental changes in the KCB; followed by (2) a detailed description of the changes in land use, crop farming, groundwater and surface water levels, and climate; and (3) associated changes in lake water surface area and salinity as well as in waterbird and fish communities during the past 40 years. The KCB is intensively farmed, and the farming of mainly water intensive crops has increased substantially, especially since 2000. This, combined with climate warming, has led to a substantial rate of reduction of the groundwater level (up to 1 m/yr) and the surface area of the lakes and wetlands, followed by an increase in salinisation, and even complete loss of several wetlands. Three globally threatened waterbird species face extinction in the basin, and 18 of the 62 previous breeding species have already been lost. The KCB has 38 fish species, of which 74% are endemic and 61% are considered threatened or near threatened. Modelling projections using various climate and land use scenarios predict serious additional reductions of the water level in the future due to climate change, leading to deterioration (or complete loss) of lake ecosystems and the services they provide.

Precipitation events determine the spatiotemporal distribution of playa surface salinity in arid regions: evidence from satellite data fused via the enhanced spatial and temporal adaptive reflectance fusion model

Playas are desert landscapes unique to arid regions that respond quickly to climate change. Changes in surface salinity in Praia are directly linked to water security and regional ecological and economic health. This study aimed to explore the sensitivity of remotely sensed spectral indices to precipitation events. An ESTARFM was utilized to fuse daily (less than 10% cloudiness) MODIS and Landsat 8 imagery from April to September 2019 in the Ebinur Lake Wetland Reserve. Salinity was tested in the laboratory after soil collections in May (spring) and August (summer). The significantly correlated normalized difference vegetation and salinity indices were compared to the precipitation data and found to fluctuate in response to precipitation. The normalized difference vegetation and salinity indices decreased following precipitation events and increased during precipitation intervals, and the precipitation amount and evaporation intensities may have influenced the magnitudes of the decrease and increase. Following precipitation, the playa surface produces new puddles and a new spatial distribution pattern of soil salinity. This study determined that the spatiotemporal fusion technique is an effective method for observing the dynamics of playa surfaces, and precipitation and evaporation affect the spatial distribution of salt on the playa surface; however, the monitoring period should be short when utilizing remote sensing to monitor playa salinity.

Projections of physical conditions in the Gulf of Maine in 2050

The Gulf of Maine (GoM) is currently experiencing its warmest period in the instrumental record. Two high-resolution numerical ocean models were used to downscale global climate projections to produce four estimates of ocean physical properties in the GoM in 2050 for the “business as usual” carbon emission scenario. All simulations project increases in the GoM mean sea surface temperature (of 1.1 °C–2.4 °C) and bottom temperature (of 1.5 °C–2.1 °C). In terms of mean vertical structure, all simulations project temperature increases throughout the water column (surface-to-bottom changes of 0.2 °C–0.5 °C). The GoM volume-averaged changes in temperature range from 1.5 °C to 2.3 °C. Translated to rates, the sea surface temperature projections are all greater than the observed 100-year rate, with two projections below and two above the observed 1982–2013 rate. Sea surface salinity changes are more variable, with three of four simulations projecting decreases. Bottom salinity changes vary spatially and between projections, with three simulations projecting varying increases in deeper waters but decreases in shallower zones and one simulation projecting a salinity increase in all bottom waters. In terms of mean vertical structure, salinity structure varies, with two simulations projecting surface decreases that switch sign with depth and two projecting increases throughout the (subsurface) water column. Three simulations show a difference between coastal and deeper waters whereby the coastal zone is projected to be systematically fresher than deeper waters, by as much as 0.2 g kg–1. Stratification, 50 m to surface, is projected to increase in all simulations, with rates ranging from 0.003 to 0.006 kg m–4 century–1 which are lower than the observed change on the Scotian Shelf. The results from these simulations can be used to assess potential acidification and ecosystem changes in the GoM.

Global-scale patterns of observed sea surface salinity intensified since the 1870s

Sea surface salinity patterns have intensified between the mid-20th century and present day, with saline areas becoming saltier and fresher areas fresher. This change has been linked to a human-induced strengthening of the global hydrological cycle as global mean surface temperatures rose. Here we analyse salinity observations from the round-the-world voyages of HMS Challenger and SMS Gazelle in the 1870s, early in the industrial era, to reconstruct surface salinity changes since that decade. We find that the amplification of the salinity change pattern between the 1870s and the 1950s was at a rate that was 54 ± 10% lower than the post-1950s rate. The acceleration in salinity pattern amplification over almost 150 years implies that the hydrological cycle would have similarly accelerated over this period.

Sea Surface Salinity Change since 1950: Internal Variability versus Anthropogenic Forcing

AbstractUsing an eastern tropical Pacific pacemaker experiment called the Pacific Ocean–Global Atmosphere (POGA) run, this study investigated the internal variability in sea surface salinity (SSS) and its impacts on the assessment of long-term trends. By constraining the eastern tropical Pacific sea surface temperature variability with observations, the POGA experiment successfully simulated the observed variability of SSS. The long-term trend in POGA SSS shows a general pattern of salty regions becoming saltier (e.g., the northern Atlantic) and fresh regions becoming fresher, which agrees with previous studies. The 1950–2012 long-term trend in SSS is modulated by the internal variability associated with the interdecadal Pacific oscillation (IPO). Due to this variability, there are some regional discrepancies in the SSS 1950–2012 long-term change between POGA and the free-running simulation forced with historical radiative forcing, especially for the western tropical Pacific and southeastern Indian Ocean. Our analysis shows that the tropical Pacific cooling and intensified Walker circulation caused the SSS to increase in the western tropical Pacific and decrease in the southeastern Indian Ocean during the 20-yr period of 1993–2012. This decadal variability has led to large uncertainties in the estimation of radiative-forced trends on a regional scale. For the 63-yr period of 1950–2012, the IPO caused an offset of ~40% in the radiative-forced SSS trend in the western tropical Pacific and ~170% enhancement in the trend in the southeastern Indian Ocean. Understanding and quantifying the contribution of internal variability to SSS trends helps improve the skill for estimates and prediction of salinity/water cycle changes.

Rapid changes in northeastern tropical Pacific Ocean surface salinity due to trans-basin moisture transport in recent decades

Argo observations revealed dramatic sea surface salinity (SSS) changes in the northeastern tropical Pacific Ocean (NETPO) during the past one and half decades, with a steady increase during 2004–2012 and a sharp decrease during 2013–2016. These changes mainly result from anomalous precipitation associated with the Walker Circulation through moisture transport across Central America. The anomalous Walker Circulation is caused by changes in trans-basin sea surface temperature (SST) gradients, especially those in the eastern tropical Pacific. Results using a longer reanalysis indicate that the upward trend of SSS in the NETPO started from the mid-1990s as the moisture transport across Central America decreased in response to reduced trans-basin SST gradients associated with the Interdecadal Pacific Oscillation and Atlantic Multidecadal Oscillation.

Mid to late-Holocene sea-surface temperature variability off north-eastern Newfoundland and its linkage to the North Atlantic Oscillation

In recent decades the surface water temperature and salinity in the Labrador Sea have been influenced by atmospheric circulation patterns, such as the North Atlantic Oscillation (NAO), as well as a trend to increasingly warm atmospheric temperatures in recent years. These changes are concerning, given the important role that temperature and salinity have on deep convection in the Labrador Sea. Yet, due to the shortness of available records, the long-term patterns of climate variability in the region are not clear. Here, a diatom-based reconstruction of summer sea-surface temperature (SST) developed from Trinity Bay, Newfoundland, provides insight into variations of SST since 7.2 cal ka BP in the southwestern Labrador Sea. The results show that the Holocene Thermal Maximum (HTM) lasted until c. 5.2 cal ka BP, which was followed by a gradual cooling trend overprinted by centennial temperature fluctuations of 1–2°C. Long-term cooling was likely the result of declining Northern Hemisphere orbital summer insolation, potentially amplified by long-term changes in surface and bottom water salinity, which led to a gradual reduction in the stratification of the water column. Centennial fluctuations in temperature vary in-phase with reconstructed variations in the NAO, supporting a consistent relationship between atmospheric circulation and SST over centennial-millennial timescales. Other factors influencing the SST variability may have been solar forcing during the mid-Holocene and variations in the strength of the subpolar gyre during the late-Holocene. The most prolonged cool period at 5.2–4.1 cal ka BP coincides with sharply reduced salinity in the Labrador Sea and a weakening of deep ventilation in the northeast Atlantic, highlighting a period with altered ocean surface conditions and circulation across the northern North Atlantic.

Muted cooling and drying of NW Mediterranean in response to the strongest last glacial North American ice surges

Abstract The massive North Atlantic iceberg discharges of the last glacial period, the so-called Heinrich events (HE), resulted in atmospheric and oceanic responses of the Mediterranean region that remain poorly documented and understood. This paper focuses on the climatic phases termed Heinrich stadials (HS) 4 and 5 generated by the HE 4 and 5 that occurred during a period of similar intermediate global ice volume and greenhouse gas concentrations but with different iceberg discharges and orbital boundary conditions. Our comparison of sea surface temperature and salinity changes with deep water conditions in the Gulf of Lions (planktonic and benthic foraminifera δ18O and δ13C records) and regional pollen-based temperature and precipitation reconstructions in NW Mediterranean for these Heinrich stadials reveal a paradoxical situation. A lower North American iceberg discharge during HS 5 compared to HS 4 is associated with colder and drier conditions in the NW Mediterranean borderlands. During the moderate iceberg discharge of HS 5 a relatively high salinity in the Gulf of Lions lead to stronger Western Mediterranean Deep Water formation and mixing of the surface with the deeper layers. By contrast during HS 4, we suggest that the massive North Atlantic iceberg break-up decreased the salinity of the Gulf of Lions and reduced the wind stress in the Mediterranean, leading to the stratification of the Mediterranean water column and inducing limited upward mixing of cold water, resulting in regional atmospheric warming and wetting compared to HS 5. This work highlights the potential crucial role of local processes in modulating the regional response to a global climate change related with ice-sheet instabilities.