ALBERT

Description: Numerous studies have evaluated the dynamics of Arctic tundra vegetation throughout the past few decades, using remotely sensed proxies of vegetation, such as the normalized difference vegetation index (NDVI). While extremely useful, these coarse-scale satellite-derived measurements give us minimal information with regard to how these changes are being expressed on the ground, in terms of tundra structure and function. In this analysis, we used a strong regression model between NDVI and aboveground tundra phytomass, developed from extensive field-harvested measurements of vegetation biomass, to estimate the biomass dynamics of the circumpolar Arctic tundra over the period of continuous satellite records (1982-2010). We found that the southernmost tundra subzones (C-E) dominate the increases in biomass, ranging from 20 to 26%, although there was a high degree of heterogeneity across regions, floristic provinces, and vegetation types. The estimated increase in carbon of the aboveground live vegetation of 0.40 Pg C over the past three decades is substantial, although quite small relative to anthropogenic C emissions. However, a 19.8% average increase in aboveground biomass has major implications for nearly all aspects of tundra ecosystems including hydrology, active layer depths, permafrost regimes, wildlife and human use of Arctic landscapes. While spatially extensive on-the-ground measurements of tundra biomass were conducted in the development of this analysis, validation is still impossible without more repeated, long-term monitoring of Arctic tundra biomass in the field.

Description: Seventy four samples of DSDP recovered cherts of Jurassic to Miocene age from varying locations, and 27 samples of on-land exposed cherts were analyzed for the isotopic composition of their oxygen and hydrogen. These studies were accompanied by mineralogical analyses and some isotopic analyses of the coexisting carbonates. d18O of chert ranges between 27 and 39%. relative to SMOW, d18O of porcellanite - between 30 and 42%. The consistent enrichment of opal-CT in porcellanites in 18O with respect to coexisting microcrystalline quartz in chert is probably a reflection of a different temperature (depth) of diagenesis of the two phases. d18O of deep sea cherts generally decrease with increasing age, indicating an overall cpoling of the ocean bottom during the last 150 m.y. A comparison of this trend with that recorded by benthonic foraminifera (Douglas and Savin, 1975; http://www.deepseadrilling.org/32/volume/dsdp32_15.pdf) indicates the possibility of d18O in deep sea cherts not being frozen in until several tens of millions of years after deposition. Cherts of any Age show a spread of d18O values, increasing diagenesis being reflected in a lowering of d18O. Drusy quartz has the lowest d18O values. On-land exposed cherts are consistently depleted in 18O in comparison to their deep sea time equivalent cherts. Water extracted from deep sea cherts ranges between 0.5 and 1.4 wt %. dD of this water ranges between -78 and -95%. and is not a function of d18O of the cherts (or the temperature of their formation).

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution June 1995

Description: This thesis addresses the question, "How do small-scale physics and biology combine to produce dense aggregations of certain species of zooplankton in the Great South Channel (GSC) of the Gulf of Maine?" The thesis consists of three relatively independent parts: an observational study made while following two right whales as they fed on dense patches of the copepod Galanus finmarchicus in the northern GSC; a detailed description of a tightly integrated set of biological and physical observations made in the GSC by means of a new instrument, the Video Plankton Recorder (VPR); and a two-dimensional Eulerian numerical model that simulates one way in which a physical flow field, combined with a biological behavior pattern, may produce dense plankton patches at a convergent front. Part I: Data from a wide variety of instruments was combined to produce a coherent picture of the physical and biological environment near two feeding right whales observed in June, 1989. Instruments included a CTD (with transmissometer), a MOCNESS net system, a 150-kHz ADCP, and a towed acoustic plankton profiler operating at 120 and 200 kHz. Acoustic data were intercalibrated with net-tow data and with "noise" in the transmissometer signal in order to estimate copepod abundance in the plankton patches on which the whales were feeding. One of the whales was observed to reverse course when copepod abundance dropped below about 1.5- 4.5 x 103 copepods/m3 , which is consistent with independent estimates of the density of copepods necessary for a right whale to gain more energy from the prey it ingests than it loses to the extra hydrodynamic drag it experiences while feeding. Part II: The VPR is a towed underwater microscope designed to image plankton non-invasively with sufficient resolution to obtain information on the spatial distribut ion of organisms on scales ranging from millimeters to hundreds of kilometers. CTD instrumentation mounted on the VPR makes it possible to correlate biological and hydrographic data with great precision. This study reports data from one transect made across the GSC in May, 1992. The data show close correlations between hydrographic features (such as fronts, plumes and water masses) and broad-scale plankton distribution. In addition, it was possible to correlate the fine-scale (order tens of meters) patchiness in plankton distribution with the local stability of the water column (as indicated by gradient Richardson number). In one case, biological data provided an aid in determining the origin of one of the observed water masses. Part III: This chapter presents a two-dimensional Eulerian numerical model that shows how depth-keeping swimming behavior on the part of an organism, combined with a convergent flow field at a surface front , can create dense patches of the organism. In this model a steady-state flow field and vertical diffusivity field are prescribed, along with the initial distribution of the plankton. The plankton swim vertically with speeds that depend only on depth, but the form of that depth-dependence may take into account such factors as the vertical variation in light level or in the concentration of some prey organism. An analysis of various nondimensional parameters associated with the model illustrates the roles played in determining the final structure of the patch by such factors as diffusion, water velocity and details of the animals' swimming behavior. Output from the model is compared with data taken at a dense plankton patch observed near a front in the northern Great South Channel in early June, 1989.

Description: My first three years in the Joint Program were paid for by the Office of Naval Research under an ONR Fellowship. I would also like to acknowledge subsequent support from the National Science Foundation under grant OCE 93-13671 and the National Oceanic and Atmospheric Administration under grants NA36GP0374 and NA26GP0431.