This study presents results of a new approach for sea floor habitat mapping based on an integrated analysis of multibeam bathymetric data, associated geoscientific information, and benthos data from Browns Bank on the southwestern Scotian Shelf, off the Canadian Atlantic coast. Based on sea floor sediment maps and statistical analysis of megabenthos determined from photographs, 6 habitats and corresponding associations of benthos were derived and mapped. The habitats are distinguished primarily on the basis of sediment type and water depth. Additional factors are sea floor geomorphology, habitat complexity, and relative current strength. A Browns Bank benthic habitat map is developed as a conceptual model summarizing the understanding of the bank ecology. This study highlights the utility of multibeam bathymetric sonar for interpretation of sea floor sediments and for extrapolating benthic habitat characteristics across large areas of sea floor.
Nearly 17 years wave records from deep water and shore-based stations are used to describe the ocean wave characteristics around New Zealand. The wave environment is dominated by west and southwest swell and storm waves generated in the temperate latitude belt of westerly winds. As a result, the west and south coasts are exposed, high energy shores, the east coast is a high energy lee shore, and the northern coast from North Cape to East Cape is a low energy lee shore sheltered from these winds and waves. South of New Zealand, wave energies are extremely high; the prevailing deep water wave is 3.5-4.5 m high and has a 10-12 s period, with a slight increase in wave heights in winter. The west coast wave environment is mixed, and consists of locally generated westerly and southerly storm waves, and swell waves generated to the south. The prevailing wave is t.0-3.0 m and 6-8 s period. There are no strong seasonal rhythms, only shorter period cycles of wave height (5 day) associated with similar quasi-rhythmic cycles in the weather. The east coast also has a mixed wave climate with southerly swells, originating in the westerlies south of New Zealand, and locally generated southerly and northerly storm waves. The prevailing wave is 0.5-2.0 m and 7-11 s period. A short period rhythmic cycle, similar to that on the west coast, is superimposed on a weak seasonal cycle. The seasonal, cycle results from an increase in the frequency of local northerly waves in summer. The prevailing wave on the north coast is a northeasterly, 0.5-1.5 m high and 5-7 s period. Subtropical disturbances and southward-moving depressions generate a mixed wave environment and a possible seasonally reflecting a winter increase in. storminess.
High-resolution seismic profiles, as well as sedimentological and micropaleontological analyses of three cores, are used to reconstruct the environmental and sedimentological evolution of Preservation Inlet, the southernmost New Zealand fjord. Toward the end of the last glaciation, a series of deep oligotrophic lakes, impounded by shallow sills, occupied Preservation Inlet. Glaciers filled the headwater valleys and the vegetation consisted of a sparse cover of grass, scrub, and shrubs. The principal rivers discharged into the head of these lakes forming large sandy deltas, while finely laminated clays were deposited in the distal basins. As the climate started warming ca. 18,000 yr B.P., the snowline rose and glaciers retreated. Developing forests were dominated by Metrosideros and Cyathea fringed by coastal shrubland. In the now more productive lakes, a rich freshwater fauna developed, sedimentation rates increased, and organic mud accumulated. Under rapidly rising sea level, between 9500 and ca. 8000 yr B.P., the sills enclosing the lakes were successively overtopped. Marine water intruded into the fjord basins and flooded the deltas at the head of the lakes. By 6500 yr B.P. sea level had stabilized and the fjord assumed its present condition. Shrubs decreased in abundance and forests dominated by Weinmannia and Dacrydium cupressinum then developed. A forest dominated by Nothofagus fusca spread between 2000 and 1500 yr B.P., indicating a cooler climate. In Preservation Inlet and other New Zealand fjords, eustatic sea-level rise has been greater than isostatic rebound or tectonic uplift. Coastal inundation has resulted in a transgressional sequence from a limnic to marine environment. This contrasts with fjord coasts of the northern hemisphere where isostatic rebound has produced coastal emergence, or coastal emergence followed by submergence.
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