River plumes are generated by the flow of buoyant river water into the coastal ocean, where they significantly influence water properties and circulation. They comprise dynamically distinct regions spanning a large range of spatial and temporal scales, each contributing to the dilution and transport of freshwater as it is carried away from the source. River plume structure varies greatly among different plume systems, depending on the forcing and geometry of each system. Individual systems may also exhibit markedly different characteristics under varied forcing conditions. Research over the past decade, including a series of major observational efforts, has significantly improved our understanding of the dynamics and mixing processes in these regions. Although these studies have clarified many individual processes, a holistic description of the interaction and relative importance of different mixing and transport processes in river plumes has not yet been realized.

How climate controls hurricane variability has critical implications for society is not well understood. In part, our understanding is hampered by the short and incomplete observational hurricane record.

[1] Rates of turbulent kinetic energy (TKE) production and buoyancy flux in the region immediately seaward ($1 km) of a highly stratified estuarine front at the mouth of the Fraser River (British Columbia, Canada) are calculated using a control volume approach. The calculations are based on field data obtained from shipboard instrumentation, specifically velocity data from a ship mounted acoustic Doppler current profiler (ADCP), and salinity data from a towed conductivity-temperature-depth (CTD) unit. The results allow for the calculation of vertical velocities in the water column, and the total vertical transport of salt and momentum. The vertical turbulent transport quantities (u 0 w 0 , S 0 w 0 ) can then be estimated as the difference between the total transport and the advective transport. Estimated production is on the order of 10 À3 m 2 s À3 , yielding a value of e(nN 2 ) À1 on the order of 10 4 . This rate of TKE production is at the upper limit of reported values for ocean and coastal environments. Flux Richardson numbers in this highly energetic system generally range from 0.15 to 0.2, with most mixing occurring at gradient Richardson numbers slightly less than 1 = 4 . These values compare favorably with other values in the literature that are associated with turbulence observations from regimes characterized by scales several orders of magnitude smaller than are present in the Fraser River.

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[1] Data collected from the near-field region (first several kilometers) of the Merrimack River plume are analyzed to provide estimates of turbulent kinetic energy (TKE) dissipation rates. Measurement techniques included a control volume method incorporating density and velocity survey data, and direct dissipation rate measurements by turbulence sensors mounted on an autonomous underwater vehicle (AUV). These two distinct observational approaches are compared with TKE dissipation rates derived from a highly resolved three-dimensional numerical model. In general, there is good agreement between the three estimates of dissipation rate. Differences occurred in two regions: (1) at the base of the plume, where plume density increased, and (2) in the very near field of the plume, which is characterized by rapid acceleration and strong shoaling. Results suggest that there is a feedback between the turbulence and the plume evolution with the result that the spreading rate of the plume is constrained. A scaling parameterization, relating turbulent dissipation rate to plume density and velocity, is also examined. Immediately seaward of the front this parameterization appears to be consistent with observed rates of dissipation, but progressing seaward, a modification to the parameterization may be necessary to account for plume spreading and deepening.

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Abstract. Human disturbance in northeastern North America over the past four centuries has led to dramatic change in vegetation composition and ecosystem processes, obscuring the influence of climate and edaphic factors on vegetation patterns. We use a paleoecological approach on Cape Cod, Massachusetts, to assess landscape-scale variation in pitch pine-oak vegetation and fire occurrence on the pre-European landscape and to determine changes resulting from European land use. Fossil pollen and charcoal preserved in seven lakes confirm a close link between landform and the pre-European distribution of vegetation. Pine forests, dominated by Pinus rigida, were closely associated with xeric outwash deposits, whereas oak-hardwood forests were associated with landforms having finer grained soils and variable topography. In general, fire was much more abundant on Cape Cod than most other areas in New England, but its occurrence varied geographically at two scales. On the western end of Cape Cod, fires were more prevalent in pine forests (outwash) than in oak-hardwood forests (moraines). In contrast, fires were less common on the narrow and north-south trending eastern Cape, perhaps because of physical limits on fire spread.The most rapid and substantial changes during the past 2000 years were initiated by European settlement, which produced a vegetation mosaic that today is less clearly tied to landform. Quercus and other hardwood trees declined in abundance in the early settlement period in association with land clearance, whereas Pinus has increased, especially during the past century, through natural reforestation and planting of abandoned fields and pastures. An increase in fossil charcoal following European settlement suggests that fire occurrence has risen substantially as a result of forest clearance and other land uses, reaching levels greater than at any time over the past 2000 years. Although fire was undoubtedly used by Native Americans and may have been locally important, we find no clear evidence that humans extensively modified fire regimes or vegetation before European settlement. Instead, climate change over the past several thousand years and European land use over the past 300 years have been the most important agents of change on this landscape.

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