Calcareous dinoflagellates from a northwestern Pacific sediment trap and their paleoceanographic implications

Abstract

Year-round changes in species composition and flux of calcareous dinoflagellates at station JT (34°09.8'N, 141°59.3'E; water depth, 8942m; trap depth, 916m) are reported. A time-series of thirteen sediment-trap samples of 29 days each, between March 5, 1991 and March 2, 1992, provided materials for this study. Vegetative cysts of a calcareous dinoflagellate, Thoracosphaera heimii, were found to be overwhelmingly dominant forming >95% of the calcareous dinoflagellate associations in all trap samples. Its' flux ranges from 910,000 shells·m -2 ·day -1 in May, 1991, to 76,000 shells·m -2 ·day -1 in September, 1991. Cysts of other calcareous dinoflagellates (Leonella granifera, Calciodinellum albatrosianum and Calciodinellum levantinum) were also found, with a maximum flux of 11,000 shells·m -2 ·day -1 for C. albatrosianum between December, 1991 and January, 1992. Based on physiological information, we suggest that species flux depends on water mass distribution linked to migration of the path of the subtropical Kuroshio Current. High to moderate flux of T. heimii occurred when the current took a meandering or a straight nearshore pathway. Waters southeast of the current prevailed over the trap station during this time. The most favorable environment, May, 1991, for T. heimii production seems to occur around a shallow thermocline formed above Subtropical Mode Water (STMW) in the waters southeast of the current. The species flux dropped when the current took an offshore pathway and flowed over the trap station. Surface and subsurface waters of the Kuroshio Current, especially during summer to autumn, is not productive of this species. The species flux also dropped while a "cold water mass" (i.e. lower salinity water cut off from the subarctic Oyashio Current) emerged over the trap station. Three cysts, L. granifera, C. albatrosianum and C. levantinum, show broadly similar abundance fluctuations to T. heimii. This close relationship between temporal changes in T. heimii productivity and path migrations of the Kuroshio Current, which is linked to the wind stress field over the North Pacific, should potentially provide information for paleoclimatic reconstructions.

TIMING DEEP DIVERGENCE EVENTS IN CALCAREOUS DINOFLAGELLATES1

“…Another corroboration of our time estimates comes from the CAL clade (containing Calciodinellum and Calcigonellum ), whose extant species are mostly restricted to coastal localities, although Calciodinellum albatrosianum is also frequent in pelagic habitats (Meier et al. 2002, Tanimura and Shimada 2004, Vink 2004, Gottschling et al. 2005b).…”

“…3) is a common element of the modern phytoplankton in the pelagial (Karwath et al. 2000, Hernández‐Becerril and Bravo‐Sierra 2004, Tanimura and Shimada 2004, Vink 2004) and is found uninterruptedly from the Late Maastrichtian onward (Kohring 1993, 1997, Hildebrand‐Habel et al. 1999, Streng et al.…”

Diversity, distribution, and new phylogenetic information of calcareous dinoflagellates from the China Sea

“…Calciodinellum elongatum has been recorded in South Atlantic and Mediterranean seas (Vink, 2004; Meier & Willems, 2003), but not in the China Sea. A sediment trap study in the west Pacific did not recover C. elongatum (Tanimura & Shimada, 2004), suggesting that this species might have a limited distribution. Calciodinellum levantinum prefers cool (13–20°C) waters (Vink, 2004), which might explain its low concentration in the South China Sea.…”

“…Sediment trap results revealed that C. albatrosianum generally produced calcareous cysts with smooth surface (Dale, 1992; Tanimura & Shimada, 2004), but in deep sea sediments, they were found to be accompanied by cysts with parasutural ridges (Meier & Willems, 2003; Vink, 2004). Details of ultrastructure from SEM observations revealed that three different types of C. albatrosianum co‐occur in the South China Sea, implying that the surface structure of C. albatrosianum might be plastic.…”

“…Thoracosphaera heimii is overwhelmingly dominant, forming >95% of the calcareous dinoflagellate associations in trap samples from the northwestern Pacific (Tanimura & Shimada, 2004). However, T. heimii accounts for less than 20% of total cyst assemblage in the South China Sea, which is consistent with the finding in equatorial Atlantic (Vink, 2004).…”