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Sprintall J.,University of California at San Diego | Gordon A.L.,Lamont Doherty Earth Observatory | Koch-Larrouy A.,LEGOS | Lee T.,Jet Propulsion Laboratory | And 4 more authors.
Nature Geoscience | Year: 2014

The Indonesian seas represent the only pathway that connects different ocean basins in the tropics, and therefore play a pivotal role in the coupled ocean and climate system. Here, water flows from the Pacific to the Indian Ocean through a series of narrow straits. The throughflow is characterized by strong velocities at water depths of about 100 m, with more minor contributions from surface flow than previously thought. A synthesis of observational data and model simulations indicates that the temperature, salinity and velocity depth profiles of the Indonesian throughflow are determined by intense vertical mixing within the Indonesian seas. This mixing results in the net upwelling of thermocline water in the Indonesian seas, which in turn lowers sea surface temperatures in this region by about 0.5 °C, with implications for precipitation and air-sea heat flux. Moreover, the depth and velocity of the core of the Indonesian throughflow has varied with the El Niño/Southern Oscillation and Indian Ocean Dipole on interannual to decadal timescales. Specifically, the throughflow slows and shoals during El Niño events. Changes in the Indonesian throughflow alter surface and subsurface heat content and sea level in the Indian Ocean between 10 and 15° S. We conclude that inter-ocean exchange through the Indonesian seas serves as a feedback modulating the regional precipitation and wind patterns. © 2014 Macmillan Publishers Limited.

Aucan J.,LEGOS | Hoeke R.,CSIRO | Merrifield M.A.,University of Hawaii at Manoa
Geophysical Research Letters | Year: 2012

Sixty years of sea-level data collected in the interior lagoon of Midway Atoll in the northern Hawaiian Islands are used to examine short-term (<2 days), high amplitude (up to 1 m) sea level anomaly (SLA) events that occur during the winter months. A combination of wind and wave model hindcasts, satellite altimetry product and in-situ water level data confirms that these high SLA events are driven primarily by the arrival of energetic swell waves generated by storms in the North Pacific as breaking waves on the northwest side of the atoll lead to the setup of the lagoon. The number of high SLA events recorded in Midway during each winter season correlates well with the storminess in the Central North Pacific, defined as the mean seasonal wave height. This leads us to conclude that the seasonal number of high SLA events measured at this specific tide gauge in Midway can be used as an index of storminess in the Central North Pacific over climatic time-scales. Our Midway-based index of storminess correlates well with the Pacific Decadal Oscillation (PDO) index, and its observed increase over the past 60 years is attributed to variability associated with the PDO rather than a long-term trend. © 2012. American Geophysical Union. All Rights Reserved.

Echevin V.,LOCEAN | Goubanova K.,LEGOS | Belmadani A.,LOCEAN | Belmadani A.,University of Hawaii at Manoa | Dewitte B.,LEGOS
Climate Dynamics | Year: 2012

The impact of climate warming on the seasonal variability of the Humboldt Current system ocean dynamics is investigated. The IPSL-CM4 large scale ocean circulation resulting from two contrasted climate scenarios, the so-called Preindustrial and quadrupling CO2, are downscaled using an eddy-resolving regional ocean circulation model. The intense surface heating by the atmosphere in the quadrupling CO2 scenario leads to a strong increase of the surface density stratification, a thinner coastal jet, an enhanced Peru-Chile undercurrent, and an intensification of nearshore turbulence. Upwelling rates respond quasi-linearly to the change in wind stress associated with anthropogenic forcing, and show a moderate decrease in summer off Peru and a strong increase off Chile. Results from sensitivity experiments show that a 50% wind stress increase does not compensate for the surface warming resulting from heat flux forcing and that the associated mesoscale turbulence increase is a robust feature. © 2011 Springer-Verlag.

Durand F.,LEGOS | Papa F.,National Oceanic and Atmospheric Administration | Rahman A.,National Oceanic and Atmospheric Administration | Bala S.K.,Bangladesh University of Engineering and Technology
Journal of Earth System Science | Year: 2011

This study investigates the impact of monthly Ganges-Brahmaputra river discharge variations on Bay of Bengal salinity and temperature during the period 1992-1999. The Ganges-Brahmaputra river discharge is characterized by a well-defined seasonal cycle with strong interannual variations. The highest/lowest yearly peak discharge occurs in summer 1998/summer 1992, with 1998 value amounting to twice that of 1992. This river discharge is then used to force an ocean general circulation model. Our main result is that the impact of these rivers on the variability of Bay of Bengal sea surface salinity is strong in the northern part, with excess run-off forcing fresh anomalies, and vice versa. Most of the years, the influence of the interannual variability of river discharge on the Bay salinity does not extend south of ~10°N. This stands in contrast with the available observations and is probably linked to the relatively coarse resolution of our model. However, the extreme discharge anomaly of 1998 is exported through the southern boundary of the Bay and penetrates the south-eastern Arabian Sea a few months after the discharge peak. In response to the discharge anomalies, the model simulates significant mixed-layer temperature anomalies in the northern Bay of Bengal. This has the potential to influence the climate of the area. From our conclusions, it appears necessary to use a numerical model with higher resolution (both on the horizontal and vertical) to quantitatively investigate the upper Bay of Bengal salinity structure. © Indian Academy of Sciences.

Oelkers E.H.,University Paul Sabatier | Gislason S.R.,Institute of Earth science | Eiriksdottir E.S.,Institute of Earth science | Jones M.,Institute of Earth science | And 2 more authors.
Applied Geochemistry | Year: 2011

A review of the relative masses of continental weathering products transported to the oceans indicates that particulate fluxes dominate dissolved fluxes for most elements. The degree to which this particulate material plays a role in the compositional evolution of seawater depends on its dissolution rate, which appears to be rapid due to its high surface area. Consideration of the results of batch experiments and mineral saturation state calculations suggest that much of the mass dissolved into seawater from particulate material dissolution is rapidly removed by the precipitation of secondary minerals. Although this process limits the degree to which the overall concentration of elements in seawater are affected by the addition of particulate material, the dissolution of isotopically distinct particulate phases may affect the isotopic composition of seawater over remarkably short timescales. © 2011 Elsevier Ltd.

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