Thierry Delcroix

• PhD
• Research Director at Institute of Research for Development

La salinité de surface de la mer (SSS : Sea Surface Salinity) influence la dynamique océanique et porte la signature du cycle de l'eau à l'interface océan-atmosphère. Pour mieux comprendre ses variations, le Service national d'observation SSS (SNO SSS) du Laboratoire d'études en géophysique et océanographie spatiales (Legos, Toulouse) gère un résea...

The signature of westward propagating mesoscale eddies in sea surface salinity (SSS) is analyzed for the tropical Pacific by collocating 7 years (2010–2016) of Soil Moisture and Ocean Salinity SSS satellite data with coherent mesoscale eddies automatically identified and tracked from altimetry‐derived sea level anomalies. First, the main characteri...

The characteristic sea surface salinity (SSS) patterns associated with the tropical Atlantic meridional and equatorial interannual modes are extracted from in situ observations, by a statistical analysis performed on the 1980–2012 period. These SSS signatures of the interannual climatic modes are reproduced in a regional numerical simulation. For e...

A current scientific issue of great interest is to understand the mechanisms leading to the localization of El Niño events either in the Central (CP) or Eastern Pacific (EP). For this, we derive a reduced gravity mixed layer model for the equatorial ocean with simple nonlinearities, diabatic effects and zonally varying background characteristics. U...

The northwestern Indian Ocean exhibits a relatively highly energetic eddy field during the southwest monsoon season between June and September. This study analyzes the seasonal and interannual variability of the eddy characteristics and their trajectories in the northwestern Indian Ocean using altimetric sea surface height observations from 1993 to...

We present a short overview of the long-term mean and variability of five Essential Climate Variables observed in the South China Sea over the last 3 decades, including sea surface temperature (SST), sea level anomaly (SLA), precipitation (P), surface wind and water discharge (WD) from the Mekong and Red Rivers. At the seasonal time scale, SST and...

L’île de Pâques continue àsusciter nombre d’interrogations, notamment quant aux origines anthropiques et/ou climatiques des changements écologiques majeurs qui se sont produits à partir du XVe siècle. Dans cet article, l’analyse combinée d’observations climatiques instrumentales (1982- 2015), d’indicateurs paléoclimatiques (1500-2000) et de simulat...

Remote sensing of salinity using satellite-mounted microwave radiometers provides new perspectives for studying ocean dynamics and the global hydrological cycle. Calibration and validation of these measurements is challenging because satellite and in situ methods measure salinity differently. Microwave radiometers measure the salinity in the top fe...

Sea level rates up to three times the global mean rate are being observed in the western tropical Pacific since 1993 by satellite altimetry. From recently published studies, it is not yet clear whether the sea level spatial trend patterns of the Pacific Ocean observed by satellite altimetry are mostly due to internal climate variability or if some...

This study focuses on the time-space variability of the low Sea Surface Salinity (SSS) waters extending zonally within 2°N-12°N in the Atlantic and Pacific and within 6°S-16°S in the western third of the Pacific. The analysis is based on a combination of in situ SSS observations collected in the last three decades from voluntary observing ships, TA...

L'expérience proposée ici a pour but de reproduire à échelle réduite le phénomène El Niño-Oscillation australe (ENSO en anglais) qui génère de fortes anomalies climatiques d'une année à l'autre, dans l'océan Pacifique tropical et au-delà, et d'en comprendre les principaux mécanismes. Elle peut être présentée à un public de collégiens, lycéens ou ét...

This study investigates the spatial trend patterns and variability of observed sea level and upper ocean thermal structure in the Pacific Ocean during the altimetry era (1993– 2012), and the role of thermocline depth changes. The ob-served sea level trend pattern in this region results from the superposition of two main signals: (1) a strong broad-...

The tropical Pacific Ocean remained in a La Niña phase from mid 2010 to mid-2012. In this study, the 2010-2011 near-surface salinity signature of ENSO (El Niño-Southern Oscillation) is described and analyzed using a combination of numerical model output, in situ data and SMOS satellite salinity products. Comparisons of all salinity products show a...

We analyze mean and seasonal change of Sea Surface Temperature (SST) and Salinity (SSS) in the Solomon and Bismarck Seas, using 1977-2009 in situ data collected from Voluntary Observing Ships. Co-variability of these two variables with surface wind, altimeter- and model-derived horizontal currents, precipitation, and Sepik River discharge are exami...

One of the leading theories to explain the oscillatory nature of the El Niño Southern Oscillation is the recharge–discharge oscillator paradigm, which roots on warm waters exchanged between the equatorial and off-equatorial regions. This study tests the relevance of this theory to account for the Eastern and recently mediated Central Pacific El Niñ...

This study investigates causes for the formation and variability of the Sea Surface Salinity maximum (SSS>36) centered near 18 degrees S-124 degrees W in the South Pacific Ocean over the 1990-2011 period at the seasonal time scale and above. We use two monthly gridded products of SSS based on in situ measurements, high-resolution along-track Volunt...

This paper investigates mechanisms controlling the mixed-layer salinity (MLS) in the tropical Pacific during 1990–2009. We use monthly 1° × 1° gridded observations of salinity, horizontal current and fresh water flux, and a validated ocean general circulation model with no direct MLS relaxation in both its full resolution (0.25° and 5 days) and re-...

Interannual global mean sea level (GMSL) variations and El Nino-Southern Oscillation (ENSO) are highly correlated, with positive/negative GMSL anomalies during El Nino/La Nina events. In a previous study, we showed that interannual GMSL and total land water storage variations are inversely correlated, with lower-than average total water storage on...

The freshest surface waters in the tropical Pacific are located near the south-east border of the Eastern Pacific Warm Pool. In this region, the seasonal migration of the Intertropical Convergence Zone (ITCZ) over the American Cordillera gives rise to monsoon-like wind and rain patterns that deeply imprint the seasonal cycle of Sea Surface Salinity...

Recent analyses of physical measurements show the existence of a central Pacific type of El Niño (CPEN) with a sea surface temperature warming pattern distinct from that of the "classical" eastern Pacific El Niño (EPEN). In this study, we analyze the surface chlorophyll signature of El Niño-Southern Oscillation (ENSO), using monthly maps of satelli...

Changes in the global water cycle are expected as a result of anthropogenic climate change, but large uncertainties exist in how these changes will be manifest regionally. This is especially the case over the tropical oceans, where observed estimates of precipitation and evaporation disagree considerably. An alternative approach is to examine chang...

The western tropical Pacific is usually considered as one of the most vulnerable regions of the world under present-day and future global warming. It is often reported that some islands of the region already suffer significant sea level rise. To clarify the latter concern, in the present study we estimate sea level rise and variability since 1950 i...

A significant surface freshening trend and an eastward expansion of fresh surface waters have been documented in the western tropical Pacific, consistent with the expected effects of climate change. The highest El Niño Southern Oscillation (ENSO) variability in Sea Surface Salinity (SSS) has been also documented in that region, with different quant...

The recent detection of a central Pacific type of El Nio has added a new dimension to the El Niño-Southern Oscillation climatic puzzle. Sea surface salinity (SSS) observations collected during 1977-2008 in the tropical Pacific are used to contrast the three eastern Pacific (EP) (1982-1983, 1991-1992, 1997-1998) and seven central Pacific (CP) (1977-...

Sea surface salinity (SSS) observations in the tropical Pacific are used to contrast the nine El Niño and four La Niña events occurring from 1977 to 2008. We show there are three Eastern Pacific (EP; 1982-83, 1991-92, and 1997-98) and six Central Pacific (CP; 1977-78, 1986-87, 1990-91, 1992-95, 2003-05, and 2006-07) types of El Niño events in terms...

The freshest waters in the tropical Pacific are found off Panama at the south-east border of the East Pacific Warm Pool. In this region, the meeting of the Intertropical Convergence Zone (ITCZ) and the American Cordillera gives birth to monsoon-like wind and rain patterns. Using more than 30 years of thermosalinograph data from ships of opportunity...

The South Pacific Convergence Zone (SPCZ), extending diagonally from Papua New Guinea to about 30°S-120°W, is a major climatic feature of the south-west tropical Pacific. It shifts north and east (south and west) of its average position during austral winter and El Niño (austral summer and La Niña), passing over the islands of Fiji (17°S-179°E) and...

A large reversal of zonal transport below the thermocline was observed over a period of 6 months in the western Pacific Ocean between 2°S and the equator [from 26.2 Sv (1 Sv ≡ 106 m3 s-1) eastward in October 1999 to 28.6 Sv westward in April 2000]. To document this reversal and assess its origin, an unprecedented collection of ADCP observations of...

This Community White Paper (CWP) examines the present Sea Surface Salinity (SSS) observing system, satellite systems to measure SSS and the requirements for satellite calibration and data validation. We provide recommendations for augmenting the in situ observing network to improve the synergism between in situ and remote sensing measurements. The...

Trends in observed sea surface salinity (SSS) and temperature are analyzed for the tropical Pacific during 1955–2003. Since 1955, the western Pacific Warm Pool has significantly warmed and freshened, whereas SSS has been increasing in the western Coral Sea and part of the subtropical ocean. Waters warmer than 28.5°C warmed on average by 0.29°C, and...

Major features of the equatorial portion of the western Pacific warm pool (WP) were brought to light through the analysis of an unprecedented collection of temperature and salinity profiles derived from Argo floats from 2000 to 2007. A region of thick (>15-25 m) and quasi-permanent barrier layers (BLs) was found to occur in a band from 10° to 20° l...

Il est désormais acquis que le réchauffement de la planète est sans équivoque (voir Giec, 2007). Des indicateurs ont ainsi été définis pour suivre et comprendre l'évolution associée de paramètres climatiques et socio-économiques à l'échelle globale et régionale. Dans ce contexte, cette étude présente l'évolution au cours des dernières décennies de...

1] Modifications of the volume of warm water above the thermocline in the equatorial Pacific are thought to be critical for ENSO (El Niño Southern Oscillation) preconditioning, development and prediction. In this paper, changes in this Warm Water Volume (WWV) are first reviewed from the literature, and then analyzed within 5°N–5°S in using 1992–200...

Sea Surface Salinity (SSS) includes relevant information about climate change and the earth's water cycle at different time and space scales. Its importance for the climate motivated the development of existing in situ observing systems and future dedicated satellite missions (SMOS and Aquarius) to enhance global observations. In this presentation,...

Sea surface salinity (SSS) data in the Atlantic Ocean is investigated between 50°N and 30°S based on data collected mostly during the period 1977–2002. Monthly mapping of SSS is done to extract the large-scale variability. This mapped variability indicates fairly long (seasonal) time scales outside the equatorial region. The spatial scales of the s...

1] The dominant mode of variability in the tropical Pacific is the interannual El Niño–Southern Oscillation phenomenon. More subtle variations are also evident on decadal timescales reminiscent of the Pacific Decadal Oscillation (PDO). These variations are superimposed on trends that are possibly linked to global climate change. A major impediment...

Sea surface salinity (SSS) data in the Atlantic Ocean is investigated between 50 degrees N and 30 degrees S based on data collected mostly during the period 1977-2002. Monthly mapping of SSS is done to extract the large-scale variability. This mapped variability indicates fairly long (seasonal) time scales outside the equatorial region. The spatial...

1] Instrumental sea surface temperature (SST) and sea surface salinity (SSS) records since 1975 have indicated that migrations of the South Pacific Convergence Zone (SPCZ) are strongly related to El Niño-Southern Oscillation (ENSO) events. To reconstruct independent SSS and SST time series for the past century and document this SPCZ and ENSO relati...

1] The upper and intermediate circulation (0– 1200 m) in the western equatorial Pacific Ocean is examined thanks to Lowered Acoustic Doppler Current Profiler (LADCP) measurements carried out during two cruises in October 1999 and April 2000. Several new features of the equatorial circulation are discussed. It is shown that the secondary South Subsu...

Recent theory suggests that ocean-atmosphere interactions in the western Pacific warm pool are of fundamental importance to interannual variations associated with El Niño and the Southern Oscillation (ENSO). The warm pool encompasses the highest mean sea surface temperatures (SSTs) in the world ocean, intense atmospheric deep convection and heavy r...

An unprecedented compilation of Sea Surface Salinity (SSS) data collected in the three tropical oceans (30°N–30°S) is examined for the period 1970–2003. The SSS data are derived mainly from 13 trans-oceanic Voluntary Observing Ship tracks and from 35 TAO/TRITON and 13 PIRATA mooring sites. Owing to the climatic importance of SSS, the data are used...

Coral skeletal geochemistry offers the potential to reconstruct the sea surface salinity (SSS) history of the tropical oceans on seasonal to interannual and perhaps centennial timescales because of the strong link between variation in SSS and seawater δ18O in tropical regions. We explore this potential using a monthly resolved, 65-year record of sk...

1] The western part of the equatorial Pacific Ocean is characterized, on average, by a relatively warm, fresh, and oligotrophic near-surface water mass, the warm pool. On its eastern side the warm pool joins cooler, saltier, and richer waters from the equatorial upwelling. Previous works have shown that the boundary between these two water masses i...

Variations in sea surface temperature (SST) and sea surface salinity (SSS) are important components of climate variability in the tropical ocean-atmosphere system. Instrumental SST time series are much more readily available than are instrumental SSS time series, which are exceedingly rare. SSS variations are strongly linked to seawater delta 18O v...

In the tropical oceans the density mixed layer does influence the ocean-atmosphere interactions, a feature that is fundamental to the development of energetic climatic events such as the El Niño-Southern Oscillation (ENSO) phenomenon. The aim of this work is to take advantage of existing sea surface temperature (SST) and velocity together with futu...

The equatorial Pacific consists of two regions that have distinct hydrological features and ecosystem dynamics: the warm pool to the west and the Pacific Equatorial Divergence (PEQD). The two regions are separated by well-defined fronts in salinity, pCO2, and macronutrients. Both the input of macronutrients in the two regions and their zonal extens...

1] Observing ocean surface salinity in the global ocean is a challenging issue for future years' oceanographic activities. It is motivated by the active role of salinity that is now well recognized in ocean dynamics and ocean/atmosphere exchanges. This is particularly evident in the case of the El Niño Southern Oscillation (ENSO) phenomenon in the...

Sea surface salinity (SSS) and sea surface temperature (SST) in the western Pacific warm pool (130-180°E 10°N-10°S) are analyzed for the period 1992-2000 taking advantage of complementary data from the ship of opportunity program and the Tropical Atmosphere-Ocean (TAO)-Triangle Trans-Ocean Buoy Network (TRITON) array of moored buoys. Covariability...

Sea surface salinity (SSS) and temperature (SST) data collected from voluntary observing ships over 25 years (1976-2000) are analyzed in the Southwestern Tropical Pacific (10°S-24°S/160°E-140°W). This region lies under the South Pacific Convergence Zone (SPCZ), at the southern edge of the western Pacific warm pool between Tahiti and Darwin, the two...

The role of the Yangtze River discharge in changing sea-surface salinity (SSS) in the East China Sea during the 1997-2001 periods is investigated by using (1) in situ SSS measurements along a merchant ship track running from Taiwan strait to Korea strait, (2) ocean general circulation model (OGCM) simulations and specific sensitivity studies, and (...

The main modes of interannual climate variability in the tropical Pacific are identified using satellite-derived wind (ERS) and sea level (TOPEX/Poseidon) data for the 1993-1999 period and output from a linear model forced by observed Florida State University (FSU) wind for the 1964-1999 period. During the 1993-1999 period a dominant El Niño-Southe...

Observing ocean surface salinity by satellite is a challenging issue for next years'oceanographic activities. It is motivated by the active role of salinity that is now well recognized in ocean dynamics and ocean/atmosphere exchanges. This is particularly evident in the case of the ENSO phenomenon in the tropical Pacific Ocean. Improvements of nume...

The impact of the strong 1997-1998 E1Nifio event on nitrate distribution and new production in the equatorial Pacific is investigated, using a combination of satellite and in situ observations, and an ocean circulation-biogeochemical model. The general circulation model is forced with realistic wind stresses deduced from ERS-1 and ERS-2 scatteromet...

We present a 60-year near-monthly record of tropical sea surface temperature (SST) during the Little Ice Age derived from coupled Sr/Ca and U/Ca analysis of a massive coral from New Caledonia (southwest tropical Pacific). The record indicates that, from 1701 to 1761, surface temperatures were on average 1.4°C cooler than during the past 30 years. T...

The eastern edge of the western Pacific warm pool corresponds to the separation between the warm, rainfall-induced low-salinity waters of the warm pool and the cold, high-salinity upwelled waters of the cold tongue in the central-eastern equatorial Pacific. Although not well defined in sea surface temperature (SST), this eastern edge is characteriz...

This paper reviews the status of the ENSO (El Niño/Southern Oscillation) Observing System, with emphasis on the Pacific Ocean during the recent 1997–98 El Niño and subsequent La Niña. Contributions of this system to detection, monitoring, forecasting, and understanding of ENSO related climate swings will be described. Recommended enhancements and e...

Les buts de la campagne FRONTALIS-01 étaient d'observer et d'améliorer la compréhension de la zone frontale située sur le bord est de la "warm pool" du Pacifique équatorial ouest tout en poursuivant la série de campagnes le long de 165°E débutée en 1984 pour appréhender la variabilité décennale. Cette campagne a eu lieu du 29 mars au 26 avril 2001,...

The role of salinity in the dynamics and thermodynamics of El Ni ס o ‐ Southern Oscillation (ENSO) events is increasingly being investigated. However, instrumental records of salinity are scarce and short in the tropical Pacific, and there is a clear need for a reliable salinity proxy to extend our knowledge of ENSO through time. Here, we present 4...

The thermal structure variability of the tropical Pacific is investigated using an objective analysis of about 250 000 temperature profiles (mainly XBT) collected during the 1979–96 time period. Mean conditions and seasonal variability are briefly described to set the context, and temperature anomalies are constructed relative to a mean seasonal cy...

In the equatorial Pacific, zonal displacements of the eastern edge of the warm pool represent an intrinsic manifestation of El Niño Southern Oscillation (ENSO) events, with numerous dynamical and biogeochemical consequences. Following a previous work dedicated to the 1986-1989 Geosat period, we focus on the 1992-1998 zonal displacements of the warm...

In the equatorial Pacific, zonal displacements of the eastern edge of the warm pool represent an intrinsic manifestation of El Niño Southern Oscillation (ENSO) events, with numerous dynamical and biogeochemical consequences. Following a previous work dedicated to the 1986-1989 Geosat period, we focus on the 1992-1998 zonal displacements of the warm...

An analysis of El Niño-Southern Oscillation (ENSO) related precipitation changes in New Caledonia, southwestern tropical Pacific, based on 21 selected stations covering the 1969-98 period is performed. The analysis at the ENSO timescale is complemented by an investigation of basin-scale precipitation changes in order to set the context, by an exami...

We present a 47-year-long record of sea surface temperature (SST) derived from Sr/Ca and U/Ca analysis of a massive Porites coral which grew at ~4150 calendar years before present (B.P.) in Vanuatu (southwest tropical Pacific Ocean). Mean SST is similar in both the modern instrumental record and paleorecord, and both exhibit El Niño-Southern Oscill...

An analysis of El Nino-Southern Oscillation (ENSO) related precipitation changes in New Caledonia, south- western tropical Pacific, based on 21 selected stations covering the 1969-98 period is performed. The analysis at the ENSO timescale is complemented by an investigation of basin-scale precipitation changes in order to set the context, by an exa...

Four years of TOPEX/Poseidon data (October 1992 to October 1996) are assimilated into a high-resolution primitive equation model [Gent and Cane, 1989] of the tropical Pacific Ocean. The assimilation method used is a degraded version of the Singular Evolutive Extended Kalman filter approach [Pham et al., 1998] in which the reduced order basis is fix...

We present a 47-year-long record of sea surface temperature (SST) derived from Sr/Ca and U/Ca analysis of a massive Porites coral which grew at ~4150 calendar years before present (B.P.) in Vanuatu (southwest tropical Pacific Ocean). Mean SST is similar in both the modern instrumental record and paleorecord, and both exhibit El Niño-Southern Oscill...

Mean conditions, seasonal, and ENSO-related (El Niño Southern Oscillation) variability in the vicinity of Wallis, Futuna, and Samoa islands (13°–15° S, 180°–170° W) over the 1973–1995 period are analysed for wind pseudo-stress, satellite-derived and in situ precipitation, sea surface temperature (SST) and salinity (SSS), sea level, and 0–450 m temp...

This paper evaluates the present role of the XBT program and proposes a strategy for the future under the assumption that there are other direct and indirect contributions to sampling the temperature and salinity of the ocean. Since the focus is on XBT sampling the paper restricts its scope to the upper ocean, mostly above 1000 m. The conclusions o...

Various data types collected in an area enclosing New Caledonia (2loS-23"S, 16O"E-17O0E) are analysed in order to assess the regional impacts of past (1972-1996) EI Niño Southem Oscillation (ENSO) events. Particular emphasis is placed on studying ENSO-related changes in sea surface temperature and salinity, surface wind stress, as well as satellite...

Seasonal and El Niño-Southern Oscillation (ENSO)-related variations of sea surface temperature (SST) and salinity (SSS), 0/450-dbar dynamic height anomalies (ε, an alias for sea level), zonal (taux) and meridional (tauy) wind stress, wind stress curl (curl (tau)), and precipitation (P) are examined in the tropical Pacific during 1961-1995. In the e...

Sea-surface salinity (SSS) changes during the 1996 La Niña and 1997 El Niño events are analysed along the Fiji-Japan shipping track, based on 20 thermosalinograph sections. In the equatorial band, above-average SSS (35.2 to 35.4 instead of 35) were observed in 1996, consistent with a well-marked south equatorial current, an unusually-strong equator...

The distribution of salt in the tropical Pacific Ocean and its variability are potentially important in better understanding the El Niño Southern Oscillation (ENSO) ocean-atmosphere coupled system. Complementary data sets (including sea surface salinity (SSS) derived from a ship-of-opportunity network, Geosat sea level and derived zonal surface cur...

Étude de la signature de l’ENSO sur les paramètres de surface de l’océan Pacifique tropical A l’échelle interannuelle, le phénomène climatique El Niño Oscillation Australe (ENSO) constitue le signal climatique le plus puissant de la Planète. Cette note décrit et analyse la variabilité associée à ce phénomène dans le Pacifique tropical au cours de...

This note aims at documenting the ENSO-related sea level changes for the whole tropical Pacific, and for the 1979-1996 period which covers numerous El Nino and La Nina events. For this purpose, we rely on (a) 0/450 dbar surface dynamic height anomaly (an alias for sea level) derived from XBT and TOGA-TAO measurements during 1979-1996, (b) TOPEX/Pos...

Data collected in an area enclosing New Caledonia are analyzed both for the open ocean (17°S-27°S, 160°E-170°E; 1972-1992) and for one point in its lagoon (1967-1993), in order to improve our knowledge of the regional environment, with emphasis on seasonal and interannual (i.e. ENSO) variability. Long-term means and seasonal changes in surface wind...