Effects of mesoscale physical processes on thin zooplankton layers at four sites along the west coast of the U.S.

Within the coastal marine environment, populations of phytoplankton, zooplankton, bacteria, viruses, and aggregations of marine snow are frequently concentrated beneath the surface in discrete, vertically thin layers. Thin layers range in vertical dimension from a few centimeters to three meters, and have been observed to extend horizontally for kilometers. They appear in the water column episodically and can persist for days. We present some of the results of an investigation of four coastal sites along the west coast of the United States to assess frequency of occurrence of thin layers of zooplankton. Our study sites included coastal sites near East Sound, Washington; Cape Perpetua, Oregon; Monterey Bay, California; and Santa Barbara, California. At each site, we collected several, weeks-long time series of hydrography, current velocity, and acoustic backscatter due to mesozooplankton. Our results show that thin layers were common features at all four sites. Across all study sites, a change in the predominant physical regime, usually precipitated by a change in the wind pattern, corresponded with an absence of thin Zooplankton layers. In order to make a first-order prediction about when thin layers have the possibility of occurring in a coastal environment, we found it useful to examine regional wind and circulation patterns and to determine how they affect stratification in each local environment.     

The shell of Mytilus as an indicator of zonal variations of water quality within an estuary

Variations in the mineralogy and chemistry of the shells of the filter-feeding organism Mytilus edulis have allowed discrimination of subenvironments of growth within the Tay estuary. Aragonite proportions higher than those predictable for the temperate, tidal, growth conditions are associated with stretches of the estuary affected by organic pollution. Accumulation and concentration of copper (Cu) in the organic periostracum suggest that Mytilus shell may also prove useful as a monitor of metallic element pollution.The relatively fragile nature of the polylayer shell of Mytilus and the layer specific distribution of components require the use of either complete, undamaged specimens or population groups to discriminate significant variations.     

Origin of the northern Atlantic's Heinrich events

As first noted by Heinrich, 1988, glacial age sediments in the eastern part of the northern Atlantic contain layers with unusually high ratios of ice-rafted lithic fragments to foraminifera shells. He estimated that these layers are spaced at intervals of roughly 10 000 years. In this paper we present detailed information documenting the existence of the upper five of these layers in ODP core 609 from 50° N and 24° W. Their ages are respectively 15 000 radiocarbon years, 20 000 radiocarbon years, 27 000 radiocarbon years, about 40 000 years, and about 50 000 years. We also note that the high lithic fragment to foram ratio is the result of a near absence of shells in these layers. Although we are not of one mind regarding the origin of these layers, we lean toward an explanation that the Heinrich layers are debris released during the melting of massive influxes of icebergs into the northern Atlantic. These sudden inputs may be the result of surges along the eastern margin of the Laurentide ice sheet.Contribution to Clima Locarno — Past and Present Climate Dynamics; Conference September 1990, Swiss Academy of Sciences — National Climate Program     

Sea-level data for parts of the Bering-Chukchi shelves of Beringia from 19,000 to 10,000 14C yr B.P.

Sea-level changes in Beringia are especially significant because they affect the migration of land plants and animals between Asia and North America, and marine plants and animals between the Pacific and Arctic oceans. Previous studies of cores from the Bering and Chukchi shelves produced sea-level curves. Evaluation of these data suggests that nine of the radiocarbon-dated estimates of sea-level position are most reliable for the time period 19,000 to 10,000 yr B.P. The trend of these nine points is proposed as the basis for a regional sea-level curve for central Beringia. Constraints on the data must be noted, however, by anyone using them.     

Their grass is greener but ours is sweeter – Thoroughbred breeding and water management in the Upper Hunter region of New South Wales, Australia

The Upper Hunter region of New South Wales (NSW) around Scone is reputed to be the second most significant thoroughbred breeding region in the world after the Bluegrass region of Kentucky. This article identifies the importance and cultural constructions of grass, and hence water, in the thoroughbred breeding industry in this region. Thoroughbred stud managers attempt to produce environments attractive to potential horse purchasers and owners with mares to be mated. These environments are constructed from perceptions of how a thoroughbred stud should appear, and from the physical conditions of specific locations. One perception is that the grass should be green. There are differing opinions in the thoroughbred breeding industry about the nutritional value of irrigated grasses, the role of these grasses in horse development and the associated access to, cost of and efficacy of water used for this purpose. The paper concludes that effective water management in this industry is only possible if various cultures of nature are understood, where necessary challenged, and subsequently included in policy and planning.     

Temporal and spatial variations in estuarine sedimentation

Sedimentation in estuaries is normally viewed as a continuous process controlled by inputs of fluvial and marine materials, which migrate in response to tidal circulation. Short-term examination yields reproducible and measurable rates of sedimentation; measurement of annual cycles reveals that sediment may be eroded from a site normally subject to deposition. Likewise annual migration patterns of turbidity maximum zones permits deposition of fine sediments at different parts of the estuary according to season. Study of long-term variations in the positions of sand banks shows that advances of the tidal flat margins may occur suddenly in response to catastrophic events; events that result in mid-channel banks becoming attached to the outer margins of the tidal flat. An example is also given of a channel-margin sand bank known to have repeatedly migrated round an elliptical path, taking approximately 25 yr to regain its original position. Long-term migration of bay head beach bars driven into the Eden Estuary and moving slowly landward are shown to create areas of temporary shelter for salt marshes, which are then over-run as the bar continues toward the head of the estuary. Several examples of anthropogenic influences on estuarine sediments are noted, with major deposits of coarse gravels attributed to known shipping trade within the Tay Estuary. Finally attention is drawn to the effects of deposition of coal mine wastes on the Fife coast: the erosion and redeposition of the wastes to form coastal platforms, their removal once mining ceased (all within a period of 90 yr), and the associated mining-induced subsidence of the coastal cliffs.     

Temporal and Spatial Variability of Freshwater Plumes in a Semienclosed Estuarine–Bay System

While the physical forcing mechanisms that govern the outflows of major rivers throughout the world are well documented in the literature, comparably less research has been done to examine the mechanisms that govern the contributions of small rivers and streams to coastal ocean systems. These rivers and streams provide a direct means for the transport of anthropogenic and terrigenous materials from watersheds to coastal oceans. This study describes the temporal and spatial variability of freshwater plumes from Kaneohe Stream, Hawaii, USA, after storm events in the Kaneohe Bay watershed. Freshwater plumes were examined using a combination of fixed moorings, synoptic shipboard surveys, and lagrangian surface drifters. Data sets were collected over the course of 19 months from August 2005 to March 2007 with particular attention paid to storms during the boreal winters. Stream discharge and duration were found to exert a primary control on plume persistence in the southern Kaneohe Bay system. Time series data show a strong coherence between wind forcing and surface currents, which, in combination with data derived from shipboard and aerial surveys, indicate that the spatial variability of freshwater plumes is primarily determined by atmospheric forcing.     

Environmental influences on the shell mineralogy ofMytilus edulis

The shells ofMytilus edulis in the Tay estuary, Scotland, show mean aragonite contents of 55%, but in one zone the average aragonite proportion is only 45%. Comparison with data forMytilus edulis from other regions indicates the temperature and salinity are not the only significant determinants of the aragonite/calcite ratio. Elimination of other variables suggests that sewage discharges may influence the mineralogy of the shell secreted byMytilus edulis in the relatively nutrient-enriched areas.