a b s t r a c tThe understanding of climate and climate change is fundamentally concerned with two things: a welldefined and sufficiently complete climate record to be explained, for example of observed temperature, and a relevant mechanistic framework for making closed and consistent inferences concerning causeand-effect. This is the case for understanding observed climate, as it is the case for historical climate as reconstructed from proxy data and future climate as projected by models. The present study offers a holistic description of northern maritime climate e from the Last Glacial Maximum through to the projected global warming of the 21st century e in this context. It includes the compilation of the most complete temperature record for Norway and the Norwegian Sea to date based on the synthesis of available terrestrial and marine paleoclimate reconstructions into continuous times series, and their continuation into modern and future climate with the instrumental record and a model projection. The scientific literature on a variable northern climate is reviewed against this background, and with a particular emphasis on the role of the Norwegian Atlantic Current e the Gulf Stream's extension towards the Arctic. This includes the introduction of an explicit and relatively simple diagnostic relation to quantify the change in ocean circulation consistent with reconstructed ocean temperatures. It is found that maritime climate and the strength of the Norwegian Atlantic Current are closely related throughout the record. The nature of the relation is however qualitatively different as one progresses from the past, through the present, and into the future.

Mass loss from the Antarctic Ice Sheet to the ocean has increased in recent decades, largely because the thinning of its floating ice shelves has allowed the outflow of grounded ice to accelerate 1,2. Enhanced basal melting of the ice shelves is thought to be the ultimate driver of change 2,3 , motivating a recent focus on the processes that control ocean heat transport onto and across the seabed of the Antarctic continental shelf towards the ice 4-6. However, the shoreward heat flux typically far exceeds that required to match observed melt rates 2,7,8 , suggesting other critical controls. Here we show that the depth-independent (barotropic) component of the flow towards an ice shelf is blocked by the dramatic step shape of the ice front, and that only the depth-varying (baroclinic) component, typically much smaller, can enter the sub-ice cavity. Our results arise from direct observations of the Getz Ice Shelf system and laboratory experiments on a rotating platform. A similar blocking of the barotropic component may occur in other areas with comparable ice-bathymetry configurations, which may explain why changes in the density structure of the water column have been found to be a better indicator of basal melt rate variability than the heat transported onto the continental shelf 9. Representing the step topography of the ice front accurately in models is thus important for simulating the ocean heat fluxes and induced melt rates. Main text: The fate of the Antarctic Ice Sheet is the greatest remaining uncertainty when predicting future sea level 10. Estimates of its contribution to global sea-level rise range from none to a catastrophic > 5 cm/year 10-12 (4 m by the year 2100). The ice sheet drains into the ocean where it terminates in floating ice shelves, overlying vast sub-ice cavities. These buttress the flow of the ice sheet, regulating the speed at which it flows into the ocean 13. Rapid thinning of ice shelves in coastal regions with warm ocean water on the continental shelf is accelerating the outflow from the ice sheet 1,2. The perceived reason-although rarely observed directly 14is that ocean currents deliver more warm water to the ice shelf cavities, causing increased basal melt. These currents originate in a reservoir of warm and salty water, known as Circumpolar Deep Water (CDW) 15 , residing at 300-1000 m depth in the Southern Ocean. Substantial amounts of dense CDW are carried onto the continental shelf by various mechanisms 4-7,16 , but only a fraction of this is needed to explain observed basal melt rates 17. The CDW flows southward in deep troughs that crosscut the continental shelf 4,18-21. The currents are steered by the bathymetry and move with shallower water to the left of the flow direction 22-24 so southward transport occurs along the eastern, and northward on western,

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<p>Shoreward oceanic heat flux in deep channels on the continental shelf typically far exceeds that required to match observed ice shelf melt rates, suggesting other critical controls.  IN the present study we study the depth-independent (barotropic) and the density-driven (baroclinic) components of the flow of warm ocean water towards an ice shelf. Using observations from the Getz Ice Shelf system as well as geophysical laboratory experiments on a rotating platform, it is shown that the dramatic step shape of the ice front blocks the barotropic component, and that only the baroclinic component, typically much smaller, can enter the sub-ice cavity.  A similar blocking of the barotropic component may occur in other areas with comparable ice-bathymetry configurations, which may explain why changes in the density structure of the water column have been found to be a better indicator of basal melt rate variability than the heat transported onto the continental shelf. Representing the step topography of the ice front accurately in models is thus important for simulating the ocean heat fluxes and induced melt rates.</p>

[1] A global ocean circulation model coupled with a simple marine ecosystem model including the biogeochemical cycles and air-sea fluxes of oxygen and carbon dioxide is used to investigate the impact of double-diffusive mixing on upper ocean physical and biogeochemical properties. By comparing results for two different parameterizations of double-diffusive mixing, we also examine the sensitivity of our estimates to the particular representation of this process in general circulation models. Differences between the two parameterizations considered turned out to be much smaller than the difference with respect to a model run without double-diffusive mixing. For both parameterizations, the impact on upper ocean temperatures and salinities is relatively small (±1°C, ±0.25 psu regionally and 0.04°C, 0.01 psu as global rms difference over the top 50 m) and changes in surface heat flux amount to 0.05 W m À2 globally. However primary production and export production in the oligotrophic subtropics are found to increase by up to 80% and 120%, respectively, when double diffusion is switched on in the model. Double-diffusive nutrient supply generates an additional oceanic carbon uptake of about 0.4 g C m À2 year À1, amounting to 0.14 Gt C year À1 globally.Citation: Glessmer, M. S., A. Oschlies, and A. Yool (2008), Simulated impact of double-diffusive mixing on physical and biogeochemical upper ocean properties,

The need to make young scientists aware of their social responsibilities is widely acknowledged, although the question of how to actually do it has so far gained limited attention. A 2-day workshop entitled "Prepared for social responsibility?" attended by doctoral students from multiple disciplines in climate science, was targeted at the perceived needs of the participants and employed a format that took them through three stages of ethics education: sensitization, information and empowerment. The workshop aimed at preparing doctoral students to manage ethical dilemmas that emerge when climate science meets the public sphere (e.g., to identify and balance legitimate perspectives on particular types of geo-engineering), and is an example of how to include social responsibility in doctoral education. The paper describes the workshop from the three different perspectives of the authors: the course teacher, the head of the graduate school, and a graduate student. The elements that contributed to the success of the workshop, and thus make it an example to follow, are (1) the involvement of participating students, (2) the introduction of external expertise and role models in climate science, and (3) a workshop design that focused on ethical analyses of examples from the climate sciences.

Women are often underrepresented in academic positions in Earth sciences (M. A. Holmes and S. O'Connell, Where are the women geoscience professors?, 2004, http:// www .eas .unl .edu/ ~ mholmes/ images/ Where %20are %20the %20Women % 20Geoscientists .pdf), with numbers below the critical mass to induce change and improve conditions. This can lead to lower productivity and a lower success rate for female scientists. However, women can overcome these problems by expanding their networks. (For background and supporting information, see the online supplement to this meeting report