Positive Sea Level Anomalies Research Articles

Special Sea‐Level and Circulation Anomalies in the Philippine Sea During the 2006/2007 and 2009/2010 El Niño Events

AbstractThe Philippine Sea (PS) tends to show sea‐level falling and cyclonic upper‐layer circulation anomalies during the developing stage (spring and summer) of El Niño, with notable influences on the circulation, climate, and biosystems of downstream regions. These changes show diversity across individual events, partly associated with El Niño‐Southern Oscillation complexity and bringing uncertainties to scientific attribution and prediction. Here, we focus on the positive sea‐level anomalies (SLAs) and anticyclonic circulation anomalies in the boreal spring and summer of 2006 and 2009, which are opposite in sign to the changes observed during other El Niño events. Correspondingly, exceptional changes were seen in downstream regions, such as the enhanced Indonesian throughflow in the Makassar Strait. Our analysis highlights the persistent equatorial easterly wind anomalies during the preceding winter, which were likely favorable for these special changes in 2006 and 2009. This is confirmed by sensitivity experiments of a simplified ocean model. The results show that the negative off‐equatorial wind stress curls in the western and central North Pacific play the key role in causing positive SLAs in the PS through evoking downwelling Rossby waves, and equatorial winds played a secondary role. Further analysis indicates that such special changes of the PS tend to take place in late‐onset weak El Niño events following the La Niña conditions.

The decadal sea level variability observed in the Indian Ocean tide gauge records and its association with global climate modes

Decadal sea level variability of the Indian Ocean is studied using long-term tide gauge observations of 17 stations. The existence of close association between Indian Ocean sea level and the global decadal climate modes, such as Pacific Decadal Oscillation (PDO) and/or Atlantic Multidecadal Oscillation (AMO) is revealed in most of the tide gauge data sets. An anti-phase sea level evolution with PDO index is identified in the regions such as west coast of India, east coast of India and the western coast of Australia. Moreover, the PDO related sea level variability is found to be stronger at the tide gauge stations along the west coast of India compared to that along the east coast of India, ruling out the remote forcing from the equatorial Indian Ocean. On the other hand, the tide gauge station at Mumbai with more than 100 years of data shows an in-phase relationship with AMO index on the decadal timescales, whereas such relationship is very weak at the tide gauge station Fremantle where similar long-term data is available. The analysis of sea level pressure (SLP), rainfall and winds over the tropical Indian Ocean indicates existence of strong relationship with AMO especially over the Arabian Sea region, strongly suggesting that the variability observed at the tide gauge station Mumbai may have larger spatial signatures. During the positive phase of AMO, the Arabian Sea region is characterized by large fall in SLP and a strong cross equatorial flow towards the Indian land mass, which are primarily responsible for the positive sea level anomalies (SLAs) at the Mumbai tide gauge station and the adjacent regions and positive rainfall over India.

Interannual Variability of Winter Sea Levels Induced by Local Wind Stress in the Northeast Asian Marginal Seas: 1993–2017

The interannual variability of winter sea levels averaged over the northeast Asian marginal seas, consisting of the Yellow Sea, East China Sea, and the East Sea (ES), was investigated. The spatial-mean sea level in winter observed using satellite altimetry shows significant interannual variations with a long-term rising trend of 3.88 mm y−1 during 1993–2017, with relatively high (Period H) and low (Period L) sea level anomalies. These anomalies correlate with the patterns of the East Asian winter monsoon at interannual timescales. The atmospheric pressure difference between the Sea of Okhotsk (SO) and ES around the Soya Strait is large during Period H. Ekman transport increases due to enhanced southeastward wind stress and results in a horizontal mass convergence that yields positive sea level anomalies during Period H. In contrast, the wind-induced transport is enhanced in the southern ES rather than in the southern SO resulting in horizontal mass divergence and negative anomalies in the spatial-mean winter sea level during Period L. Our results highlight the important roles of local wind forcing and Ekman dynamics in inducing interannual winter sea level variability in the region indicating the high predictive ability of atmospheric pressure anomalies around the Soya Strait.

Interactions Between Mesoscale Eddies and Synoptic Oscillations in the Bay of Bengal During the Strong Monsoon of 2019

AbstractThe 2019 southwest monsoon season is the first strong monsoon in the last 25 years and occurred concurrently with a strong positive Indian Ocean Dipole (pIOD). Given these unique circumstances, we examine the mesoscale eddy field in the Bay of Bengal (BoB) during 2019 and the interactions between these eddies and 3–7‐day synoptic oscillations and tropical systems, which contribute to monsoon rainfall and modulate the active (wet) and break (dry) phases of the Indian monsoon. We find that there is a drastic difference in eddy characteristics between the western (80–90°E) and eastern (90–100°E) BoB, where eddies in the eastern BoB are dominated by coastal Kelvin wave (CKW) dynamics and topographical influences, and the eddies in the western BoB are more heavily modulated by East India Coastal Current dynamics. We further find that the pIOD increased the overall sea level in the BoB and modified CKW propagation in the BoB such that all eddy types had more positive sea level anomalies. We find that cyclonic eddies vary coherently with both upper ocean heat content and 3–7‐day bandpass filtered precipitation and that both the number of cyclonic eddies and eddy amplitude increase in coherence with precipitation and ocean heat content following the passage of a tropical system. These results suggest a strong relationship between cyclonic eddies and 3–7‐day atmospheric variability.

Importance of Resolving Mesoscale Eddies in the Model Simulation of Ningaloo Niño

AbstractSatellite observational data and a regional ocean model are used to understand the evolution of Ningaloo Niño (NN) anomalies near Western Australian coast. In observation and high‐resolution (~3 km) simulations, coastally trapped positive sea level anomalies (SLAs), originated largely from the Indonesian Throughflow, are transmitted westward by mesoscale eddies. Few eddies propagate long distances offshore due to dissipation, and as a result NN signatures are predominantly confined near the coast. In coarse‐resolution (~100 km) simulations that cannot resolve eddies, oceanic anomalies propagate swiftly as long Rossby waves with much weaker dissipation and more anomalies spread to the ocean interior. Eddy‐enhanced surface warming promotes surface latent heat release and mesoscale air‐sea interactions, which acts to damp NN surface warming. These processes are not resolved by coarse‐resolution models. This study highlights the importance of resolving mesoscale oceanic processes in the simulation and prediction of NN.

Sea level anomalies in the northwestern Pacific during 2011 associated with La Niña and negative Indian Ocean Dipole

The sea level anomalies (SLAs) pattern in the northwestern Pacific delineated significant differences between La Nina events occurring with and without negative Indian Ocean Dipole (IOD) events. During the pure La Nina events, positive the sea surface level anomalies (SLAs) appear in the northwestern Pacific, but SLAs are weakened and negative SLAs appear in the northwestern Pacific under the contribution of the negative IOD events in 2010/2011. The negative IOD events can trigger significant westerly wind anomalies in the western tropical Pacific, which lead to the breakdown of the pronounced positive SLAs in the northwestern Pacific. Meanwhile, negative SLAs excited by the positive wind stress curl near the dateline propagated westward in the form of Rossby waves until it approached the western Pacific boundary in mid-2011, which maintained and enhanced the negative phase of SLAs in the northwestern Pacific and eventually, it could significantly influence the bifurcation and transport of the North Equatorial Current (NEC).

The effect of cyclones crossing the Mediterranean region on sea level anomalies on the Mediterranean Sea coast

Abstract. Large positive and negative sea level anomalies on the coast of the Mediterranean Sea are linked to intensity and position of cyclones moving along the Mediterranean storm track with dynamics involving different factors. This analysis is based on a model hindcast and considers nine coastal stations, which are representative of sea level anomalies with different magnitudes and characteristics. When a shallow water fetch is present, the wind around the cyclone centre is the main cause of positive and negative sea level anomalies, depending on its onshore or offshore direction. The inverse barometer effect produces a positive anomaly on the coast near the cyclone pressure minimum and a negative anomaly at the opposite side of the Mediterranean Sea. The latter is caused by the cross-basin mean sea level pressure gradient that is associated with the presence of a cyclone. This often coincides with the presence of an anticyclone above the station, which causes a local negative inverse barometer effect. Further, at some stations, negative sea level anomalies are reinforced by a residual water mass redistribution within the basin, which is associated with a transient response to the atmospheric pressure forcing. Though the link with the presence of a cyclone in the Mediterranean has comparable importance for positive and negative anomalies, the relation between cyclone position and intensity is stronger for the magnitude of positive events. The area of cyclogenesis, track of the central minimum and position at the time of the event differ depending on the location the sea level anomaly occurs and on its sign. The western Mediterranean is the main cyclogenesis area for both positive and negative anomalies overall. Atlantic cyclones mainly produce positive sea level anomalies in the western basin. At the easternmost stations, positive anomalies are caused by cyclogenesis in the eastern Mediterranean. North African cyclogenesis is a major source of positive anomalies on the central African coast and negative anomalies on the eastern Mediterranean and northern Aegean coasts.

Characterizing habitat suitability for a central-place forager in a dynamic marine environment.

Characterizing habitat suitability for a marine predator requires an understanding of the environmental heterogeneity and variability over the range in which a population moves during a particular life cycle. Female California sea lions (Zalophus californianus) are central‐place foragers and are particularly constrained while provisioning their young. During this time, habitat selection is a function of prey availability and proximity to the rookery, which has important implications for reproductive and population success. We explore how lactating females may select habitat and respond to environmental variability over broad spatial and temporal scales within the California Current System. We combine near‐real‐time remotely sensed satellite oceanography, animal tracking data (n = 72) from November to February over multiple years (2003–2009) and Generalized Additive Mixed Models (GAMMs) to determine the probability of sea lion occurrence based on environmental covariates. Results indicate that sea lion presence is associated with cool (<14°C), productive waters, shallow depths, increased eddy activity, and positive sea‐level anomalies. Predictive habitat maps generated from these biophysical associations suggest winter foraging areas are spatially consistent in the nearshore and offshore environments, except during the 2004–2005 winter, which coincided with an El Niño event. Here, we show how a species distribution model can provide broadscale information on the distribution of female California sea lions during an important life history stage and its implications for population dynamics and spatial management.

Trans-equatorial migration and non-breeding habitat of tropical shearwaters: implications for modelling pelagic Important Bird Areas

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 550:219-234 (2016) - DOI: https://doi.org/10.3354/meps11713 Trans-equatorial migration and non-breeding habitat of tropical shearwaters: implications for modelling pelagic Important Bird Areas Fiona McDuie*, Bradley C. Congdon Centre for Tropical Environmental and Sustainability Science & College of Marine & Environmental Science, James Cook University, MacGregor Rd, Smithfield, Cairns, QLD 4870, Australia *Corresponding author: fionamcduie@gmail.com ABSTRACT: Declining prey availability drives many seabirds to migrate following breeding. While long-distance, latitudinal migrations are common in temperate-breeding species (including temperate-breeding Procellariiformes), regional dispersal or longitudinal migration is more common in tropical-breeding species. We used geolocators to track adult, tropical-breeding wedge-tailed shearwaters Ardenna pacifica from the Great Barrier Reef, Australia, through a ~6000 km migration to non-breeding grounds in Micronesia. This lengthy, trans-equatorial migration was similar to that undertaken by temperate-breeding Procellariiformes, but contrasted with patterns previously observed for tropical-breeding species. However, the oceanographic characteristics of tropical non-breeding habitats differed significantly from those of temperate sites. Core-use habitat had high sea-surface temperatures, very low wind speeds and low primary productivity, features normally associated with poor foraging habitat. However, activity was strongly linked to positive sea-level anomalies, indicating the presence of anti-cyclonic eddies at foraging sites. Such eddies are often associated with oceanic fronts and are known to aggregate micronekton and facilitate sub-surface predator feeding. Consequently, our results suggest that eddies, frontal activity and feeding associations with sub-surface predators enhance prey availability to non-breeding shearwaters beyond levels expected based on standard indices of primary production. This is the first tropical study to simultaneously assess the full set of oceanographic features considered important for modelling pelagic Important Bird Areas (IBA). Our findings demonstrate the need for IBA modelling in the tropics to go beyond standard indices of productivity by including measures of frontal activity and assessments of biological interactions. Consequently, this study provides a framework for better predicting candidate Marine IBAs throughout tropical regions. KEY WORDS: Overwinter · Tropical Procellariiform · Sea-level anomalies · Sub-surface predator · Electronic tracking · Marine Important Bird Areas (MIBAs) · Habitat modelling Full text in pdf format PreviousNextCite this article as: McDuie F, Congdon BC (2016) Trans-equatorial migration and non-breeding habitat of tropical shearwaters: implications for modelling pelagic Important Bird Areas. Mar Ecol Prog Ser 550:219-234. https://doi.org/10.3354/meps11713 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 550. Online publication date: May 25, 2016 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2016 Inter-Research.

Analyzing the physics of non-tidal barotropic sea level anomaly events using multi-scale numerical modelling in Singapore regional waters

The hydrodynamic flows in the Singapore regional waters (SRW) are the result of a complex mix of tide, seasonal and meteorological effects. The study of non-tidal effects or sea level anomalies (SLA) in this region has shown that it is possible to model some of these anomalies. The present study addresses the non-tidal barotropic water levels and currents in the Singapore region in detail. This analysis includes a multi-scale approach, and addresses amongst others hydrodynamic model grid resolution and the importance of resolving non-linear tide–surge interaction. The results show that the water level and current anomalies phenomena in a complex region like SRW can be effectively modelled using an approach combining non-tidal barotropic and multi-scale numerical modelling. A detailed investigation of the levels of non-linear tide–surge interaction is carried out by simulating SLA events in the Singapore regional waters during North-East (positive SLA) and South-West (negative SLA) monsoons based on ECMWF numerical weather forcing conditions. The results of combining both approaches suggest that the finer grid resolution improves the accuracy of water level and current anomalies simulations. Furthermore, the results also indicate that for the simulations of non-tidal barotropic flows in this area, non-linear tide–surge interaction is important and should be taken into account. Finally, the behaviour of the non-tidal barotropic flow in the region and its changes with tidal variation in the shallow region of the Singapore Strait is now much better understood. Therefore, for reliable operational forecast of sea level, the inclusion of non-linear tide–surge interaction should be required in numerical models to reproduce both tides and surges with improved accuracy in this region.

Surface signature of Mediterranean water eddies in the Northeastern Atlantic: effect of the upper ocean stratification

Abstract. Meddies, intra-thermocline eddies of Mediterranean water, can often be detected at the sea surface as positive sea-level anomalies. Here we study the surface signature of several meddies tracked with RAFOS floats and AVISO altimetry. While pushing its way through the water column, a meddy raises isopycnals above. As a consequence of potential vorticity conservation, negative relative vorticity is generated in the upper layer. During the initial period of meddy acceleration after meddy formation or after a stagnation stage, a cyclonic signal is also generated at the sea-surface, but mostly the anticyclonic surface signal follows the meddy. Based on geostrophy and potential vorticity balance, we present theoretical estimates of the intensity of the surface signature. It appears to be proportional to the meddy core radius and to the Coriolis parameter, and inversely proportional to the core depth and buoyancy frequency. This indicates that surface signature of a meddy may be strongly reduced by the upper ocean stratification. Using climatic distribution of the stratification intensity, we claim that the southernmost limit for detection in altimetry of small meddies (with radii on the order of 10–15 km) should lie in the subtropics (35–45° N), while large meddies (with radii of 25–30 km) could be detected as far south as the northern tropics (25–35° N). Those results agree with observations.

Habitat preference, accessibility, and competition limit the global distribution of breeding Black-browed Albatrosses

Telemetry methods and remote sensing now make it possible to record the spatial usage of wide-ranging marine animals and the biophysical characteristics of their pelagic habitats. Furthermore, recent statistical advances mean that such data can be used to test ecological hypotheses and estimate species' distributions. Black-browed Albatrosses Thalassarche melanophrys are highly mobile marine predators with a circumpolar breeding and foraging distribution in the Southern Hemisphere. Although they remain relatively abundant, increased fisheries bycatch has led to their listing as endangered by conservation bodies. We satellite-tracked 163 breeding Black-browed Albatrosses and eight closely related Campbell Albatrosses T. impavida from nine colonies. We then quantified habitat usage, and modeled population-level spatial distribution at spatiotemporal scales >50 km and 1 month, as a function of habitat accessibility, habitat preference, and intraspecific competition, using mixed-effects generalized additive models (GAMM). During incubation, birds foraged over a wider area than in the post-brood chick-rearing period, when they are more time constrained. Throughout breeding, the order of habitat preference of Black-browed Albatrosses was for neritic (0–500 m), shelf-break and upper shelf-slope (500–1000 m), and then oceanic (>1000 m) waters. Black-browed Albatrosses also preferred areas with steeper (>3°) bathymetric relief and, in addition, during incubation, warmer sea surface temperatures (peak preference ∼16°C). Although this suggests specialization in neritic habitats, incubation-stage Black-browed Albatrosses from South Georgia also foraged extensively in oceanic waters, preferring areas with high eddy kinetic energy (>250 cm2/s2), especially the Brazil-Malvinas Confluence, a region of intense mesoscale turbulence. During chick-rearing, this species had a more southerly distribution, and following the seasonal retreat of sea ice, birds from some populations utilized neritic polar waters. Campbell Albatrosses showed similar bathymetric preferences but also preferred positive sea level anomalies. Black-browed Albatross foraging areas were partially spatially segregated with respect to colony and region, with birds preferring locations distant from neighboring colonies, presumably in order to reduce competition between parapatric conspecifics. At the global scale, the greatest concentrations of breeding Black-browed Albatrosses are in southern South American neritic, shelf-break, and shelf-slope waters. These regions also hold large fisheries and should therefore be a priority for introduction of bycatch mitigation measures.

Nivel relativo del mar en la costa pacífica sur de Colombia: variabilidad, tendencias e implicaciones en la dinámica deltaica

According to the relative sea level (RSL) data series from Tumaco 1953-2006, the positive sea-level anomalies show a good coherence with the Southern Oscillation lndex (SOI). The variability of the SOI explains 61 % of the seasonal variability in the water level data (r2 = 0.61, &lt; 0.05). Maximum peaks appear in the 1982-1983 and 1997-1998 El Nino years, which were approximately 30 cm above the interannual monthly mean. The long term sea-level trend was decreasing at 0.60 mm/yr. Two subgroups of sea-level data with changing trends were identified: first (1953-1979), a decreasing trend of 4.7 mm/yr; second, an increasing trend rising at a rate of 4.7 mm/yr. The break of the series coincides with the occurrence of the 1979 great Tu maco earthquake (Mw = 8.2). That rate of change in the RSL subgroups could be explained through the theoretical dislocation model of strain accumulation and release at a subduction zone. Moreover, anomalies in water discharge of the Mira River (1981-2002) show an incrementally higher discharge in the drainage river basin between 1981 and 1987 and a diminishing trend in the discharge between 1988 and 2002. Recent delta dynamics show a continuous progradation proceeding between 1958 and 1987. After the 1979 earthquake, relative sea leve! rise, the 1982-1983 El Nino events and decreased river input may explain the change to a slow coastal erosion stage at the delta front.

El Niño and sea level anomalies: a global perspective

The anomalous weather patterns observed world‐wide associated with El Niño are often accompanied by changes in local sea levels. Sea level anomalies are transmitted through various oceanic and atmospheric pathways and data suggest that this effect is currently on the order of tens of centimetres in some areas both within and outside of the equatorial Pacific. Positive sea level anomalies either generated or enhanced by El Niño have been linked to powerful storm waves and coastal flooding.

Influence of temperature and precipitation on decadal Baltic Sea level variations in the 20th century

It is known that interannual Baltic Sea level variations in the 20th century can be partially, but not totally, explained by the wind forcing linked to the North Atlantic Oscillation (NAO) and other atmospheric circulation patterns. Using regression analysis linking sea level variations (as predictand) and sea level pressure (SLP), precipitation and air temperature (included stepwise as predictors) it is investigated to what extent precipitation and temperature variations can also contribute to explain Baltic sea level variability, in addition to SLP. In wintertime, their additional contribution is small compared to that of SLP (of the order of additional 15% of variance), but it is statistically significant and their inclusion as predictors help to explain past deviations in the evolution of sea level, with higher than normal temperatures and precipitation values linked to a positive contribution to sea level anomalies. In summer, temperature and precipitation explain a substantial part of the sea level variability except in the Kattegat region. In summer positive sea level anomalies are linked to higher than normal rainfall but to lower than normal temperatures, suggesting that the statistical link between sea level and temperature may artificially arise by the observed negative correlation between temperature and rainfall. For some stations, temperature and precipitation can explain, in addition to the variance explained by SLP alone, 35% of the total variability. Since part of influence of temperature and precipitation might be already contained in SLP, this value represents a lower limit for the influence of these additional factors on sea level variability. However, recent trends of winter sea level in the last 20 yr cannot be described by a linear model with any of the predictors used in this study.

Anatomy of three warm-core Leeuwin Current eddies

Abstract The vertical structures of three warm-core Leeuwin Current eddies are described, as well as their temporal evolution determined from altimetric data. These warm-core eddies have large positive sea-level anomalies, although their surface temperature fields are not necessarily warmer than the ambient waters. These eddies were observed some 350 km offshore from the Leeuwin Current in September 2000, around 25–30°S, and their vertical structure and temporal evolution show they were formed at the coast in May, when the Leeuwin Current is strongest. After separation from the current, the warm-core eddies drifted WNW following isopycnal contours, and were strongly steered by bathymetry. These eddies penetrated to at least 1500 m depth; the strongest eddy, Eddy B, influenced isopycnals to 2500 m. Eddy B appeared to be trapped and intensified by a Leeuwin Current squirt that directed warm, low-salinity water offshore from August to October. The average annual eddy heat and salt fluxes for waters warmer than 8°C are estimated at 0.004 PW and 3×10 5 kg s −1 , respectively. The magnitude of these eddy fluxes is 20–30% of the annual mean poleward heat and salt flux in the eastern Indian Ocean, and is within the range of values observed for Agulhas eddies entering the South Atlantic.

Recent evolution of sea-level extremes at Trieste (Northern Adriatic)

The evolution of sea-level extremes at Trieste (Northern Adriatic) is analysed for the 1939–2001 period by studying the occurrence of positive and negative surges and positive and negative anomalies of observed sea level. Marked interannual and multiannual fluctuations are recognized, which can be related to the observed changes in the atmospheric pressure and wind regimes that affected the Adriatic region in the period of interest. Over the period under study, weak and moderate surges of both signs do not exhibit a clear trend, while the frequency of both strong positive and negative surges tends to decrease. Weak and moderate positive sea-level anomalies become more frequent, while all negative anomalies tend to exhibit a negative trend, because of the superposition of the general mean sea-level rise on the surge evolution. One consequence is that the frequency of strong positive anomalies, among which flood events, appears to be almost stable. The role of the anomalous behaviour of sea-level extremes observed in the winters 1989–1993, as a consequence of persisting atmospheric pressure anomalies, is also investigated.

Análisis de las condiciones oceanográficas y metereológicas de la Bahía de Tumaco y su relación con eventos de escala global

The interannual and seasonal variability of the bahía de Tumaco (Tumaco Bay) has been studíed by oceanographic and meteorological measurements, from 1999 and 1992. During this period of time, it could be determined a cycle with two well defined conditions; the first one, from February to mid- April, as a cold phase, with seawater column (0 to 100 m) temperatures between 13.6 and 26° C, the rising of the thermocline and halocline (Oto 20 m) to the surface and a higher nutrient concentraron; and the other phase, the rest of the year, with warmer waters, between 14 and 27.8° C and a deeper thermocline and halocline (30 to 50 m). This annual cycle is due the presence of the Intertropical Convergence Zone, ITCZ, at the Eastern Equatorial Pacific región, consistently with the stress of the Northeastern and Southeastern Trade Winds and its surface currents. This cycle was affected by global events, like the equatorial Kelvin waves of first baroclinique mode, during April-May, that rose the sea surface temperature, SST, the air temperature and rains; La Niña 1999-2000 event, that caused lower SST valúes (26.5° C), negative sea level anomalies and the highest nutrients concentraron of the observed time, nitrites (0.2 pM), phosphates (2pM), silica (50pM) and ammonia (4pM); and from September 2002 by El Niño event, identified by the positivesea level anomalies (more than 10cm), higher than normal rains and air temperature and the deepening of the 15°C isotherm.

Seasonal and interannual thermohaline variability in the Guaymas Basin of the Gulf of California

Temperature and salinity data for the years 1939–1983 are used to investigate seasonal and interannual scales of the hydrographic variability across the Guaymas Basin, which is located between 27° and 28°N in the Central Gulf of California. Winter conditions extend from December to April and summer conditions from June to October, with transition periods in May and November. Sea surface temperature increases from about 16°C in February–March to 31°C in August. No clear seasonal cycle in surface salinity was found. Typical values are above 35.1‰ even in winter, and up to 35.5‰ in November. Relatively cold and low salinity near-surface waters observed in June 1957 and in June 1982, suggest advection of California Current Water to the Guaymas Basin. Subtropical Subsurface Water may occur around the year, but is obscured by vertical mixing with Gulf Water mainly during winter, when vertical stratification is weaker. The Intermediate and Deep Pacific Water masses successively fill the Guaymas Basin to the bottom (2000 m), showing very stable T-S characteristics. Positive sea level anomalies at Guaymas increases during El Nin˜o years, and anomalous low salinity and high temperature at the surface indicate the presence in the Guaymas Basin of water from the south. Observed differences reached 0.4‰ in surface salinity and 3°–5°C in surface temperature. There is evidence that the observed low salinities could not be due to abundant precipitation. An additional effect is a deepening of the winter pycnocline down about 200 m, compared to the usual depth of <100 m. In summer, this effect is not as clear as in winter, due to the strong stratification. The effects of the very strong 1982–1983 and 1957–1958 ENSO episodes may have lasted for one and two years, respectively. It is argued that during an ENSO event the Transition Water of the California Current meet and mix near the Gulf entrance with the Tropical Surface Water of the Costa Rica Coastal Current. This mixed water could have been carried north into the Gulf by local surface circulation. In 1983 it was found at the surface in the Guaymas Basin above the southeastward flow of the colder and saltier Gulf Water.