891 research outputs found
The importance of planetary rotation period for ocean heat transport
The climate, and hence potential habitability, of a planet crucially depends on how its atmospheric and oceanic circulation transports heat from warmer to cooler regions. However, previous studies of planetary climate have concentrated on modelling the dynamics of their atmospheres whilst dramatically simplifying the treatment of the oceans, which neglects or misrepresents the effect of the ocean in the total heat transport. Even the majority of studies with a dynamic ocean have used a simple so-called aquaplanet having no continental barriers, which is a configuration which dramatically changes the oceanic dynamics. Here the significance of the response of poleward ocean heat transport to planetary rotation period is shown with a simple meridional barrier – the simplest representation of any continental configuration. The poleward ocean heat transport increases significantly as the planetary rotation period is increased. The peak heat transport more than doubles when the rotation period is increased by a factor of ten. There are also significant changes to ocean temperature at depth, with implications for the carbon cycle. There is strong agreement between the model results and a scale analysis of the governing equations. This result highlights the importance of both planetary rotation period and the ocean circulation when considering planetary habitability
Geochemical proxies of ocean circulation and weathering inputs: Radiogenic isotopes of Nd, Pb, Sr, Hf, and Os
Marine records of the radiogenic isotope composition of the elements neodymium (Nd), lead (Pb), hafnium (Hf), strontium (Sr), and osmium (Os) allow the reconstruction of past ontinental weathering inputs on different time scales as a function of their respective oceanic residence times. Sr and Os have oceanic residence times significantly longer than the global mixing time of the ocean and are efficiently mixed on a global scale. Their isotope composition changes on long time scales as a function of plate tectonics and major orogenies, which allows their use as precise stratigraphic tools for the entire Phanerozoic. In contrast, Hf, Pb, and in particular Nd, have residence times on the order of or shorter than the global mixing time of the ocean, which results in distinct isotopic signatures of water masses and allows the reconstruction of past water mass mixing and weathering inputs on both long and short time scales. Here applications of these isotopes systems with a focus on the shorter residence time tracers are reviewed (without claiming to be comprehensive) and problems and potential solutions are discussed. Keywords: Radiogenic isotopes, paleo-oceanography, ocean circulation, water mass mixing, continental weatherin
Wind Forced Variability in Eddy Formation, Eddy Shedding, and the Separation of the East Australian Current
The East Australian Current (EAC), like many other subtropical western boundary currents, is believed to be penetrating further poleward in recent decades. Previous observational and model studies have used steady state dynamics to relate changes in the westerly winds to changes in the separation behavior of the EAC. As yet, little work has been undertaken on the impact of forcing variability on the EAC and Tasman Sea circulation. Here using an eddy‐permitting regional ocean model, we present a suite of simulations forced by the same time‐mean fields, but with different atmospheric and remote ocean variability. These eddy‐permitting results demonstrate the nonlinear response of the EAC to variable, nonstationary inhomogeneous forcing. These simulations show an EAC with high intrinsic variability and stochastic eddy shedding. We show that wind stress variability on time scales shorter than 56 days leads to increases in eddy shedding rates and southward eddy propagation, producing an increased transport and southward reach of the mean EAC extension. We adopt an energetics framework that shows the EAC extension changes to be coincident with an increase in offshore, upstream eddy variance (via increased barotropic instability) and increase in subsurface mean kinetic energy along the length of the EAC. The response of EAC separation to regional variable wind stress has important implications for both past and future climate change studies
Proceedings 'The Colour of Ocean Data': international symposium on oceanographic data and information management with special attention to biological data Brussels, Belgium, November 25-27, 2002
The Colour of Ocean Data: International Symposium on oceanographic data and information management, with special attention to biological data. Brussels, Belgium, 25-27 November 2002: book of abstracts
Ocean data management plays a crucial role in global as well as local matters. The Intergovernmental Oceanographic Commission -with its network of National Oceanographic Data Centres- and the International Council of Scientific Unions- with its World Data Centres- have played a major catalysing role in establishing the existing ocean data management practices. No one can think of data management without thinking of information technology. New developments in computer hard- and software force us to continually rethink the way we manage ocean data. One of the major challenges in this is to try and close the gap between the haves and the have-nots, and to assist scientists in less fortunate countries to manage oceanographic data flows in a suitable and timely fashion. So far major emphasis has been on the standardisation and exchange of physical oceanographic data in open ocean conditions. But the colour of the ocean data is changing. The ‘blue’ ocean sciences get increasingly interested in including geological, chemical and biological data. Moreover the shallow sea areas get more and more attention as highly productive biological areas that need to be seen in close association with the deep seas. How to fill in the gap of widely accepted standards for data structures that can serve the deep ‘blue’ and the shallow ‘green’ biological data management is a major issue that has to be addressed. And there is more: data has to be turned into information. In the context of ocean data management, scientists, data managers and decision makers are all very much dependent on each other. Decision makers will stimulate research topics with policy priority and hence guide researchers. Scientists need to provide data managers with reliable and first quality controlled data in such a way that the latter can translate and make them available for the decision makers. But do they speak the same ‘language’? Are they happy with the access they have to the data? And if not, can they learn from each other’s expectations and experience? The objective of this symposium is to harmonize ocean colours and languages and create a forum for data managers, scientists and decision makers with a major interest in oceanography, and open to everyone interested in ocean data management
Surface salinity of the North Atlantic : can we reconstruct its fluctuations over the last one hundred years ?
Surface samples have been collected in the North Atlantic in the past one hundred years for determining the ocean salinity and its temperature. A large share of the data we have used were collected by merchant vessels of weather ships of European countries and to a large extent are listed in reports, in particular in the "Bulletin Hydrographique". We investigate whether these data are relevant for determining low frequency fluctuations of the sea surface salinity. We find many crossing in the 1920s for which salinity is anomalously high compared with the climatology or with other crossings collected on the same ship line. These anomalies are indicative of a contamination of the sample. By examining hydrographic data, reports and recent experience in collectionand storage in sea water, we can attribute these large errors to unclean buckets where salt crystals dissolve into the sample and to breathing of the samples during the storage. Each of these stages contributes in estimating a too large salinity and adds to the scatter of the measurements. (D'après résumé d'auteur
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