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

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

IOC contributions to international, interdisciplinary open data sharing

Author Posting. © Oceanography Society, 2010. This article is posted here by permission of Oceanography Society for personal use, not for redistribution. The definitive version was published in Oceanography 23, no. 3 (2010): 140-151, doi: 10.5670/oceanog.2010.29Over the last 50 years, the Intergovernmental Oceanographic Commission (IOC) has had a profound influence upon the willingness of United Nations Member States to share and provide access to their international and interdisciplinary oceanographic data. (For an early history and review of IOC achievements, see Roll, 1979.) Ocean science over the last half century has been transformed from a predominately modular, single-disciplinary, and individualistic science into a national and multinational interdisciplinary enterprise (Briscoe, 2008; Powell, 2008). The transformation began slowly, but as computing power increased, the pace accelerated, and along with these alterations came shifts in cultural practices regarding the sharing of data

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

The role of the basic state in the ENSO-monsoon relationship and implications for predictability

The impact of systematic model errors on a coupled simulation of the Asian Summer monsoon and its interannual variability is studied. Although the mean monsoon climate is reasonably well captured, systematic errors in the equatorial Pacific mean that the monsoon-ENSO teleconnection is rather poorly represented in the GCM. A system of ocean-surface heat flux adjustments is implemented in the tropical Pacific and Indian Oceans in order to reduce the systematic biases. In this version of the GCM, the monsoon-ENSO teleconnection is better simulated, particularly the lag-lead relationships in which weak monsoons precede the peak of El Nino. In part this is related to changes in the characteristics of El Nino, which has a more realistic evolution in its developing phase. A stronger ENSO amplitude in the new model version also feeds back to further strengthen the teleconnection. These results have important implications for the use of coupled models for seasonal prediction of systems such as the monsoon, and suggest that some form of flux correction may have significant benefits where model systematic error compromises important teleconnections and modes of interannual variability

Ocean heat uptake and its consequences for the magnitude of sea level rise and climate change

Under increasing greenhouse gas concentrations, ocean heat uptake moderates the rate of climate change, and thermal expansion makes a substantial contribution to sea level rise. In this paper we quantify the differences in projections among atmosphere-ocean general circulation models of the Coupled Model Intercomparison Project in terms of transient climate response, ocean heat uptake efficiency and expansion efficiency of heat. The CMIP3 and CMIP5 ensembles have statistically indistinguishable distributions in these parameters. The ocean heat uptake efficiency varies by a factor of two across the models, explaining about 50% of the spread in ocean heat uptake in CMIP5 models with CO2 increasing at 1%/year. It correlates with the ocean global-mean vertical profiles both of temperature and of temperature change, and comparison with observations suggests the models may overestimate ocean heat uptake and underestimate surface warming, because their stratification is too weak. The models agree on the location of maxima of shallow ocean heat uptake (above 700 m) in the Southern Ocean and the North Atlantic, and on deep ocean heat uptake (below 2000 m) in areas of the Southern Ocean, in some places amounting to 40% of the top-to-bottom integral in the CMIP3 SRES A1B scenario. The Southern Ocean dominates global ocean heat uptake; consequently the eddy-induced thickness diffusivity parameter, which is particularly influential in the Southern Ocean, correlates with the ocean heat uptake efficiency. The thermal expansion produced by ocean heat uptake is 0.12 m YJ−1, with an uncertainty of about 10% (1 YJ = 1024 J)

Marine biogeochemical responses to the North Atlantic Oscillation in a coupled climate model

In this study a coupled ocean-atmosphere model containing interactive marine biogeochemistry is used to analyze interannual, lagged, and decadal marine biogeochemical responses to the North Atlantic Oscillation (NAO), the dominant mode of North Atlantic atmospheric variability. The coupled model adequately reproduces present-day climatologies and NAO atmospheric variability. It is shown that marine biogeochemical responses to the NAO are governed by different mechanisms according to the time scale considered. On interannual time scales, local changes in vertical mixing, caused by modifications in air-sea heat, freshwater, and momentum fluxes, are most relevant in influencing phytoplankton growth through light and nutrient limitation mechanisms. At subpolar latitudes, deeper mixing occurring during positive NAO winters causes a slight decrease in late winter chlorophyll concentration due to light limitation and a 10%–20% increase in spring chlorophyll concentration due to higher nutrient availability. The lagged response of physical and biogeochemical properties to a high NAO winter shows some memory in the following 2 years. In particular, subsurface nutrient anomalies generated by local changes in mixing near the American coast are advected along the North Atlantic Current, where they are suggested to affect downstream chlorophyll concentration with 1 year lag. On decadal time scales, local and remote mechanisms act contemporaneously in shaping the decadal biogeochemical response to the NAO. The slow circulation adjustment, in response to NAO wind stress curl anomalies, causes a basin redistribution of heat, freshwater, and biogeochemical properties which, in turn, modifies the spatial structure of the subpolar chlorophyll bloom

A dynamic explanation for the origin of the western Mediterranean organic-rich layers

The eastern Mediterranean sapropels are among the most intensively investigated phenomena in the paleoceanographic record, but relatively little has been written regarding the origin of the equivalent of the sapropels in the western Mediterranean, the organic-rich layers (ORLs). ORLs are recognized as sediment layers containing enhanced total organic carbon that extend throughout the deep basins of the western Mediterranean and are associated with enhanced total barium concentration and a reduced diversity (dysoxic but not anoxic) benthic foraminiferal assemblage. Consequently, it has been suggested that ORLs represent periods of enhanced productivity coupled with reduced deep ventilation, presumably related to increased continental runoff, in close analogy to the sapropels. We demonstrate that despite their superficial similarity, the timing of the deposition of the most recent ORL in the Alboran Sea is different than that of the approximately coincident sapropel, indicating that there are important differences between their modes of formation. We go on to demonstrate, through physical arguments, that a likely explanation for the origin of the Alboran ORLs lies in the response of the western Mediterranean basin to a strong reduction in surface water density and a shoaling of the interface between intermediate and deep water during the deglacial period. Furthermore, we provide evidence that deep convection had already slowed by the time of Heinrich Event 1 and explore this event as a potential agent for preconditioning deep convection collapse. Important differences between Heinrich-like and deglacial-like influences are highlighted, giving new insights into the response of the western Mediterranean system to external forcing