Diatom-inferred productivity changes in the eastern equatorial Pacific: The Quaternary record of ODP Leg 111, Site 677

Schrader, Hans; Swanberg, Neil R.; Lycke, Anne Katrine; Paetzel, Matthias; Schrader, Tim; Schrader, Thies

doi:10.1007/978-94-017-3622-0_16

Cited by 7 publications

(10 citation statements)

References 12 publications

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“…3c). Due to its resistance to dissolution, high abundances of this species in coastal sediments have been regarded as representing otherwise severely dissolved diatom assemblages (Schrader et al, 1993). In spite of this, the abundance of Paralia sulcata in the sediments of the Galician northern shelf may reflect not only its preferential preservation in strong dissolution conditions but also the distinct effects of upwelling along the coast.…”

Section: Discussionmentioning

confidence: 99%

Mesoscale distribution patterns of diatoms in surface sediments as tracers of coastal upwelling of the Galician Shelf (NW Iberian Peninsula)

1997

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Diatom distribution on continental shelf sediments from the upwelling area off Galicia (NW Iberian Peninsula) has been determined in 78 surface sediment samples. Three well defined biofacies with a close relationship to upwelling influence along the coast have been distinguished from both the absolute diatom abundances in the sediments and assemblage diatom composition based on multivariate statistics: Rias Baixas and the shelf areas south and north to Cape Finisterre. Chaetoceros resting spores as well as highest absolute diatom content in the sediments are recorded in the highly productive Rias Baixas where most of the primary production is due to intense upwelling phenomena. The western shelf, south of Cape Finisterre, is characterized by Thalassionema nitzschioides and Thalassiosira cf. leptopus. Both taxa reflect a minor influence of upwelling conditions and productivity related to more persistent nutrient input due to coastal outwelling rather than upwelling. Minor and patchy upwelling conditions as well as lower productivity in the northern shelf are characterized by the lowest absolute diatom content in the sediments and the important increase in relative abundance of the resistant Paralia sulcata. Caution must be taken in the interpretation of Paralia sulcata dominated biofacies in downcore studies since a juxtaposition of discontinuous upwelling conditions and dissolution effects may be the factors responsible for the relative increase on the taxon in the sediments. The obtained resultsshow the extent and limitations of fossil diatom distribution in surface sediments as tracers of regional coastal upwelling conditions in continental shelves where the existence of extensive areas of relict sediments and transported diatoms may mask the present-day upwelling signal of the photic zone.

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Section: Discussionmentioning

confidence: 99%

Mesoscale distribution patterns of diatoms in surface sediments as tracers of coastal upwelling of the Galician Shelf (NW Iberian Peninsula)

1997

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“…These results are not unexpected considering the preferred habitat of the organisms studied. Diatoms are known to compete well in high-nutrient, cold water upwelling systems [Schrader et al, 1993;Guillard and Kilham, 1977] such as existed in the Cariaco Basin region during the YD. In fact, it has been shown that diatoms bloom only when silicate concentrations are _> 2 gM/kg [Egge and Aksnes, 1992], thus the necessity for strongly upwelling waters.…”

Section: 21mentioning

confidence: 99%

Climate-induced variations in productivity and planktonic ecosystem structure from the Younger Dryas to Holocene in the Cariaco Basin, Venezuela

Werne¹

2000

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A high-resolution molecular organic geochemical study of sediments in the anoxic Cariaco Basin indicates significant changes in primary productivity and planktonic community structure associated with the transition from the Younger Dryas to the Holocene. Variations in climate conditions over the past 12 •4C kyr have induced large-scale changes in upwelling intensity, which directly affected levels of primary productivity as reflected in accumulation rates of bulk productivity proxies. Concentrations and accumulation rates of sterol and alkenone biomarkers have been used to identify how productivity changes affected the structure of the planktonic ecosystem. A shift in the dominant primary producer from diatoms (Younger Dryas) to coccolithophores (Holocene) is identified. If productivity and ecosystem variations like those identified in the tropical upwelling zone of the Cariaco Basin region, occur throughout the tropical oceans, they have the potential to affect global climate through perturbations in the biogeochemical cycle of carbon. cold period (11-10 •4C kyr), in low-latitude settings in both continental [cf. Islebe et al., 1995; Troelstra et al., 1995] and marine environments [cf. Flower and Kennett, 1990; Keigwin and Jones, 1990; Kennett, 1990; Linsley and Thunell, 1990; Peterson et al., 1991; Hughen et al., 1996a, b; Hughen et al., face temperature (SST) recorded at higher latitudes. For example, Hughen et al. [1996a, b] presented high-resolution correlations between sedimentological signals inferred to reflect productivity in the Cariaco Basin and signals from both ice cores and high-latitude lacustrine sediments. Thus it appears that global climate change may be manifested as variations in productivity in low-latitude environments where temperature variations are less significant. The correlations presented by Hughen et al. [1996a, b] and others provide compelling evidence for a low-latitude response to global climate perturbations. If global climate changes such as the YD cold period are indeed manifested in the tropical oceans primarily as variations in productivity, they should be recognizable in sediments such as those in the Cariaco Basin that tend to preserve organic matter (OM) and/or inorganic indicators of productivity (e.g., carbonate and opal remains) at high resolution.In order to examine changes in biological productivity and the planktonic community structure we have undertaken an organic geochemical study in sediments deposited over the last 12 kyr in the Cariaco Basin. Our goal was to assess climateinduced change in the intensity of primary productivity and 1998]. Some of these low-latitude climate signals have been the structure of the planktonic ecosystem assemblage within positively correlated w•_th •arhatmns m •ce •olume and sea sur-•,. ,with the transition from YD to Holocene. Molecular (bio-Paper number 1998PA000354. marker) accumulation rates have been used to identify unambi-0883-8305/00/1998PA000354512.00 guously the source(s) of the organic matter (i.e., marine versus

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“…However, the diatom assemblage in the massive sections has strikingly high abundances of several large, heavily silicified taxa, (A. nodulifera itself, large Coscinodiscus, Chaetoceros diadema spores), and a notable absence of more weakly silicified taxa, which are present in the laminated sections (e.g., Rhizosolenia, Bacteriastrum). Central gyre sedi-ments, where A. nodulifera is most abundant [Schrader et al, 1993], are characterized by poor preservation of diatoms. The high abundance of this species downcore therefore may be in part determined by differential dissolution of the assemblage.…”

Section: Glacial-interglacial Changesmentioning

confidence: 99%

Diatoms in the Gulf of California: Seasonal flux patterns and the sediment record for the last 15,000 years

Sancetta¹

1995

Paleoceanography

121

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Flux and taxonomic composition of the diatom assemblage was determined for biweekly sediment traps in the central Gulf of California over a 2‐year period. Fluxes and relative abundance of taxa are not significantly different in traps from the eastern side of the Guaymas Basin and the western side of the Carmen Basin, indicating that patterns of diatom production are uniform across the central gulf at all seasons of the year. The annual maximum in diatom flux occurred during the winter season of both years, either as a sustained event over many weeks (1990) or as a series of short blooms (1991–1992). Of the most abundant taxa, only hyalochaete Chaetoceros species showed a clear seasonal cycle, with a flux maximum in the spring of both years. Factor analysis defines five assemblages representing (1) summer and fall conditions of surface stratification and nutrient limitation, (2) winter bloom triggered by onset of strong northwesterly winds, (3) late spring to summer production probably related to sporadic events during periods of weak southeasterly winds, (4) spring 1991 inferred to reflect the distal edge of a coastal upwelling phase, (5) lateral advection of resuspended sediments from the continental shelf, possibly resulting from trapped coastal waves during summer hurricanes and from storms during the 1991–1992 El Niño‐Southern Oscillation (ENSO). The diatom data support the inference that subtropical Pacific water penetrates deeper into the gulf during ENSO events. In order to compare the sediment trap record to a sediment core, a second factor analysis was done using only the taxa which are preserved in the sediment and omitting the most abundant taxa, which showed little downcore variation. This produces five factors representing (1) summer‐fall low production, (2) early winter bloom, (3) late winter‐spring upwelling, (4) ENSO conditions and (5) a late spring‐summer assemblage of uncertain significance. Variation of species characterisic of each factor was examined in piston core Atlantis II 125‐8 56JPC taken from the oxygen minimum zone in Guaymas Basin. Correlation to nearby Deep Sea Drilling Project Hole 480 indicates that the core penetrates to about 15 ka, with laminated sediments in the Holocene (0–10 ka) and late deglacial (11–13 ka) and massive (nonlaminated) sediments around Younger Dryas time (10–11 ka) and before 13 ka. Downcore variations in the diatom assemblage do not correspond directly to presence of laminations, implying that the processes controlling bottom water oxygen content are not determined by conditions of surface water production. Presence of calcareous nannofossils downcore correlates inversely with two diatom assemblages (ENSO and winter bloom indicators) and not with occurrence of laminations, suggesting that occurrence of calcareous nannofossils in the sediment is at least partly a function of surface water production. Prior to 12 ka, production was lower than at present during all seasons, implying weaker winds throughout the year; subtropical waters extended to the midgulf as...

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Diatom-inferred productivity changes in the eastern equatorial Pacific: The Quaternary record of ODP Leg 111, Site 677

Cited by 7 publications

References 12 publications

Mesoscale distribution patterns of diatoms in surface sediments as tracers of coastal upwelling of the Galician Shelf (NW Iberian Peninsula)

Mesoscale distribution patterns of diatoms in surface sediments as tracers of coastal upwelling of the Galician Shelf (NW Iberian Peninsula)

Climate-induced variations in productivity and planktonic ecosystem structure from the Younger Dryas to Holocene in the Cariaco Basin, Venezuela

Diatoms in the Gulf of California: Seasonal flux patterns and the sediment record for the last 15,000 years

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