OS42A-01
Physical Limnology, the Master and the Servant
Physical Limnology has matured to the point where a fairly complete inventory of processes and their dynamical description is now available. To illustrate this, I will present a brief summary of the processes underlying the response of the water column to a sudden wind event and show how this may be quantified using the Wedderburn and Burger numbers. These knowledge is making it possible to provide the biogeochemist with a quantitative description of the transport and mixing of their state variables. New advances in field instrumentation has allowed real time self learning modelling of both the physics and the biogeochemistry. Currently we are adding real time DNA analysis opening up the possibility of measuring in-situ growth rates at the species level. Together these tools are allowing the prediction of both the population parameters of the state variables and for times out to the autocorrelation times, the state variable itself. After describing this, I will conclude with a brief look at the new challenge in environmental management of lakes and other domains; the inability of humans to make the right decisions.
OS42A-02
Rock dissolution, soils, and riverine solute fluxes to the world's oceans
Seawater chemistry responds to changes in terrestrial weathering over time in response to the forcing functions of tectonism, climate, and anthropogenic activity. Many researchers have attempted to read the effects of weathering solute fluxes in sediments in the rock record. For example, the Sr isotope record in marine limestones has been interpreted with respect to continental weathering fluxes. In contrast, our ability to predict such fluxes forward in time is limited because of difficulties in calculating weathering fluxes and the rates of formation of soils on weathering or eroding bedrock. Weathering solute fluxes are recorded in many areas as chemical and textural profiles imprinted on regolith. These profiles, when observed on noneroding regolith, propagate downward as the regolith pile thickens with time. Such a profile can be described as a quasi-stationary state. If the rate of erosion of such regolith is increased larger than the weathering advance rate, the regolith thickness must decrease with time. For such a condition, the regolith eventually disappears unless some process accelerates the weathering advance rate. However, during weathering, as regolith thins, the rate of weathering advance increases because porefluid chemistry becomes more corrosive. Thus, the rates of erosion and weathering advance can be coupled through porefluid chemistry, maintaining regolith thickness at steady state values. Solute fluxes and regolith profiles can be predicted for simplified lithologies under these assumptions. The weathering advance rate is not, however, observed to be the same when calculated at the watershed, soil profile, and hand specimen scales. Several phenomena contribute to this observation. Approaches will be described to understand the prediction and modeling of weathering advance rates across scales as well as the controls on weathering solute fluxes to the world's oceans.
OS42A-03
Ocean Circulation and Mixing: New Insights From the Global Distribution of 3He
Since the discovery of mantle 3He in the ocean in the 1960's by Clarke and others this isotope has been used in numerous studies of ocean circulation and mixing. Recently, a global helium isotope data set has been collected during the World Ocean Circulation Experiment (WOCE). We combined the WOCE helium isotope data with similar, but smaller, data sets from previous global and regional studies such as GEOCSECS or TTO to study features of the global ocean circulation, as well as ventilation and mixing. In this contribution we describe the global data set and discuss the first results obtained on global ocean ventilation and deep ocean mixing. A simple model is used to estimate vertical turbulent exchange coefficients for the deep ocean in the South Pacific and the results are compared to mixing coefficients obtained from fine structure measurements and tracer release experiments.
OS42A-04
Observing and Modelling the Greenland Scotland Overflow
The overflows across the Greenland -Scotland Ridge system are an important component of the Atlantic Meridional Overturning Circulation, Both, observing and modelling the overflow is a challenging task, because relatively small spatial scales are involved. The physics of the overflow is governed by rotating hydraulics, a process that has not been represented in large scale climate models until recently. We report on experiments to capture the overflows by new observational techniques and show that an advanced coupled climate model resolving the Denmark Strait with an appropriate grid confirms the nonlinear hydraulic character. Overflow variations can be linked to upstream reservoir height changes and - in case of the Denmark Strait - also to sea surface elevation, providing a possibility to monitor the throughflow with remote sensing techniques. Finally, a controlled volume box model based on hydraulic exchange laws is used to analyse overflow variability during the last century and to compare results with observations.
OS42A-05
The "rain of particles" into the deep sea: perspectives of a biological detective who sifts through oceanic sediment traps
The sedimentation of particles from the ocean's sunlit zone to underlying waters is not only key to sustenance of life at depth but also to the sequestration of carbon and surface-derived materials in underlying waters and sediments. Decades of research on particle flux have provided considerable quantitative information about the chemical constituents of sinking materials and their vertical and horizontal variability in the oceans. The biological processes initiating the rain have also received considerable attention, and models demonstrate the importance of particular characteristics of the photosynthetic organisms that initiate the process, as well as the features of the food webs that may control delivery rates. In this presentation, I revisit discoveries dating from sediment trap studies of the early ‘80s to those of the recent VERTEX project to decipher what the contents of sediment traps, particularly the various photosynthetic and other unicellular organisms, can tell us about biological processes affecting the rain of particles into the deep ocean.