PHYSICAL OCEANOGRAPHY PROJECTS


Upper ocean fronts

The ocean surface is filled with a convoluted web of fronts that separate waters of different temperatures and salinities. Just as alveoli facilitate rapid exchange of gases in the lungs, fronts are the ducts through which heat, carbon, oxygen and other climatically important tracers enter into the deep ocean. Fronts can be as narrow as hundreds of meters and as wide as tens of kilometers. In our group we develop theories to understand the role of fronts on Earth’s climate and we participate in field campaigns [read here]. We are also collaborating with NASA to develop a new altimeter to observe fronts from space, the Surface Water Ocean Topography mission [read here].


Ocean mesoscale eddies

The ocean circulation is dominated by geostrophic eddies, i.e. cyclones and anticyclones with radii of 10-100 kilometers. These eddies are the ocean equivalent of the storms we experience in the atmosphere as weather. Eddies play an important role in the transport of heat, carbon and other climatically important tracers across the oceans. Our group is very active in this research area and we develop theories for the physics of ocean eddies, their role in climate, and their representation in numerical models used for climate studies [read here]. Prof. Ferrari lead a Climate Process Team aimed at improving the representation of ocean eddies in climate models. Our group is also involved in a field campaigns: the Southern Ocean, the Diapycnal and Isopycnal Mixing Experiment whose goal is to measure eddy mixing in the Southern Ocean [read here], and the Climate Mode Water Experiment focused on the role of eddies in the formation of intermediate waters [read here].


Ocean vertical mixing

Seawater sinks around Antarctica because the cold temperatures make it so dense that it plunges to the ocean bottom. These waters are then brought back up to the surface by turbulent mixing. Turbulence consists of rapid erratic motions like the ones we feel on a rough airplane ride, or, which we generate with a spoon when we try to mix sugar in coffee. The turbulent motions mix the cold waters back to the surface much like giant spoons stirring the ocean abyss. Our group studies what processes drive this turbulent mixing.


Ocean heat transport

The ocean contributes to regulating the Earth's climate through its ability to transport heat from the equator to the poles. Our group studies the role of winds in driving this heat transport, an important question for climate and climate change [read here]. We also study the role of tropical cyclones (hurricanes) in driving ocean heat transport. Contrary to recent speculations, we find that topical cyclones are not likely to have modified the ocean heat transport in the present or past climates [read here].


The energy cycle of the ocean circulation

The ocean circulation is the result of a balance between wind forcing and air-sea fluxes at large scales and dissipation at small scales. A full theory of the circulation must therefore include a discussion of the processes that take the energy from the forcing to the dissipation scales, also known as the turbulent cascade. Our group is trying to develop such a theory with a combination of theory, large scale ocean models and observations. We find that the turbulent cascade plays an important role in setting the response of the ocean circulation to changes in Earth's climate [read here].



PALEO-OCEANOGRAPHY PROJECTS


Ocean circulation at the last Glacial maximum

The ocean’s role in regulating atmospheric carbon dioxide on glacial-interglacial timescales remains a primary unresolved issue in studies of paleoclimate. We are investigating whether changes in ocean circulation and ocean mixing may have aided storage of atmospheric CO2 at the Last Glacial Maximum [read here].



BIOGEOCHEMISTRY PROJECTS


Ocean eddies and biology

Ocean eddies sets the physical and chemical environment of ocean ecosystems on space scales of kilometers and time scales of days, through its lateral stirring of tracers and control of nutrient supply by vertical motions. Indeed one can think of the ocean eddies as an "evolutionary hot-spot" in time and space for life in the ocean. Just as it is not a coincidence that elemental ratios in seawater are the same as those in life, so the life cycle of phytoplankton is in synchrony with mesoscale physics. Thus, eddies may well be a key determinant of the structure and function of the entire marine foodweb: the average structure of marine ecosystems may reflect the integrated, and rectified, effects of mesoscale processes, modulating primary production, community structure and hence the export of organic carbon to the interior ocean. The mesoscale circulation and life within it, acts and interacts locally, and yet has global consequences for climate. There is thus an inevitable disconnect between observations and process models which, of necessity, focus on regional descriptions, and climate questions which demand knowledge of integrated effects. In our research we attempt to link across these scales.


Phytoplankton blooms

The annual cycle of phytoplankton growth in many parts of the ocean is dominated by a rapid, intense population explosion in late winter or early spring, the so-called spring bloom. The increase in the phytoplankton population associated with the spring bloom accounts for up to a third of the annual phytoplankton production and contributes significantly to the carbon flux to the deep ocean. The spring bloom occurs globally in coastal seas, lakes, in the Mediterranean and Black Seas, and most famously in the North Atlantic where the associated change in ocean color can easily be seen from space. Our group is currently studying what physical conditions prompt the onset of a bloom.