Dinoflagellate cysts and acritarchs from California current surface sediments
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Three aspects of Recent dinoflagellate cyst and acritarch paleoecology in the California Current are examined in the present study. First the biogeography of these palynomorphs is described from seventy surface sediment samples distributed from 480 to 240 N latitude. Then yearly variations in the cyst deposition in varved Santa Barbara Basin sediments are documented and compared with historical oceanographic variations. Finally, the systematics of the dinoflagellate cysts and acritarchs are presented. Six regions within the California Current were studied; aquatic palynomorphs varied in peak abundance as follows: Baja California > Southern California Bight = Gulf of California > Washington Shelf > San Juan Islands > Central California. One region, the Washington Shelf is characterized by abundant freshwater or enigmatic palynomorphs, while marine dinoflagellates and acritarchs dominate the others. Large scale dinoflagellate cyst abundance variations can be attributed partly to variations in annual seasonal amplitude in oceanographic factors, which influences the ratio of cyst forming to non-cyst forming dinoflagellates. In addition, the hydrographic regime is more conducive to dinoflagellate growth in the southern areas. Within the Southern California Bight and Gulf of California, abundance variations are due to a complex interaction of production, sedimentation and preservation. The most important dinocyst group in the region is the genus Spiniferites, with several different species reaching dominance. Linguloginium machaerophorum is the most abundant cyst in the Southern California Bight, however. Broad similarity is seen in assemblages from the six areas, with a general tendency to add species to the flora during the flow of the current south and into the Gulf of California. Most of the forms found in the San Juan Islands, Washington Shelf and Central California persist into the southern regions. In comparing these cyst floras to published planktonic dinoflagellate censuses, several species are either over-or underrepresented in sediments. To determine whether distinctive dinocyst communities could be detected in particular geographic areas a two way indicator species analysis was run. This hierarchical technique of clustering, based on reciprocal averaging, revealed interregional differences in community composition and delineated oceanographically determined cyst regions. The Washington Shelf was separated from all others based on a predominance of freshwater palynomorphs. Other distinctive regions include the Inshore Southern California Bight (dominated by L. machaerophorum), the Offshore Oregon Region (Impasidinium spp.), and the Southern Current, Baja California and Gulf of California Region (Spiniferites spp. and others). Smaller Subregions and areas within these divisions were also detected, based on subtler cyst community differences. The species groupings obtained from the analysis comprised a range from the northern and freshwater forms, through widely distributed species, to the strictly southern dinocysts. Yearly variations in cyst abundance from dated Santa Barbara Basin varves representing sediment deposited in the years 1925 to 1910 A.D. were dooumented. Wide fluotuations in total and individual speoies annual influx were found which were compared to the years of known blooms of cyst-forming dinoflagellates and published sea surface temperature time series, including records of oceanwide El Nino occurrences. Lingulodinium machaerophorum, Spiniferites spp. and total cyst abundanoe apparently respond negatively to annual sea surface temperature. In addition, some blooms of Gonyaulax Polyedra follow recorded peaks in deposition of its cyst. It is proposed that the responses of these two major cyst types to fluctuations in current advection upwelling and temperature differ due to their divergent eoology and inferred survival strategies. The palynologioal examination yielded 64 species of palynomorphs ot whioh 33 are existing species, 25 are described using open or cf.-type nomenclature and six are proposed as new. Three new genera are also proposed. Abundance distribution maps ot signifioant species are also presented.