Characteristics of alkenone distributions in suspended and sinking particles in the northwestern North Pacific

Harada, Naomi; Sato, Miyako; Shiraishi, Aya; Honda, Makio C.

doi:10.1016/j.gca.2006.01.024

Cited by 44 publications

(37 citation statements)

References 54 publications

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“…5c). This phenomenon has been previously reported for the northern Mediterranean Sea (Ternois et al, 1997), the central Arabian Sea (Prahl et al, 2000), the subtropical North Pacific (Prahl et al, 2005;Popp et al, 2006) and the subarctic NW Pacific (Harada et al, 2006) and has been attributed to either alkenone production at the thermocline depth (Ternois et al, 1997;Harada et al, 2006) or nutrient deficiency (Popp et al, 2006). Culture experiments have shown a decrease in U K' 37 with nutrient deficiency (Epstein et al, 1998;Conte et al, 1998a;Yamamoto et al, 2000a).…”

Section: Season and Depth Of Alkenone Productionsupporting

confidence: 81%

“…Ohkouchi et al (1999) argued that alkenones record the temperatures within or below the thermocline (~150 m deep) because the alkenone temperatures in surface sediments were nearly 10°C lower than annual mean SSTs in the overlying water in the subtropical Pacific. In the subarctic Pacific, Harada et al (2006) reported that U K' 37 -based temperatures in sinking particles corresponded with the thermocline temperatures during the high export season, while they were higher than SSTs during the low export season.…”

Section: Introductionmentioning

confidence: 97%

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Seasonal and depth variations in molecular and isotopic alkenone composition of sinking particles from the western North Pacific

Yamamoto

Shimamoto²,

Fukuhara³

et al. 2007

Deep Sea Research Part I: Oceanographic Research Papers

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Abstract:Seasonal and depth variations in alkenone flux and molecular and isotopic composition of sinking particles were examined using a 21-month time-series sediment trap experiment at a mooring station WCT-2 (39°N, 147°E) in the mid-latitude NW Pacific to assess the influences of seasonality, production depth, and degradation in the water column on the alkenone unsaturation index U K' 37 . Analysis of the underlying sediments was also conducted to evaluate the effects of alkenone degradation at the 1 water-sediment interface on U K' 37 . Alkenone sinking flux and U K' 37 -based temperature showed strong seasonal variability. Alkenone fluxes were higher from spring to fall than they were from fall to spring. During periods of high alkenone flux, the U K' 37 -based temperatures were lower than the contemporary SSTs, suggesting alkenone production in a well-developed thermocline (shallower than 30m). During low alkenone flux periods, the U K' 37 -based temperatures were nearly constant and were higher than the contemporary SSTs. The nearly constant carbon isotopic ratios of C 37:2 and C 38:2 alkenones suggest that alkenones produced in early fall were suspended in the surface water until sinking. The alkenone sinking flux decreased exponentially with increasing depth. The decreasing trend was enhanced during the periods of high alkenone flux,suggesting that fresh and labile particles sank from spring to fall, while old and stable particles sank from fall to spring. The U K' 37 -based temperature usually increased with increasing depth. The preservation efficiency of alkenones was ~2.7-5.2% at the water-sediment interface. Despite the significant degradation of the alkenones, there was little difference in U K' 37 levels between sinking particles and the surface sediment.

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Section: Season and Depth Of Alkenone Productionsupporting

confidence: 81%

Section: Introductionmentioning

confidence: 97%

Seasonal and depth variations in molecular and isotopic alkenone composition of sinking particles from the western North Pacific

Yamamoto

Shimamoto²,

Fukuhara³

et al. 2007

Deep Sea Research Part I: Oceanographic Research Papers

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“…High concentrations of C 37:4 are associated with the cooler and fresher water masses found in the Pacific subarctic [Harada et al, 2006]. The correlation between %C 37:4 and SSS in the Pacific subarctic was strong (R 2 = 0.76), although the relationship was insignificant for %C 37:4 versus SST (R 2 = 0.17; [Bendle et al, 2005;Harada et al, 2006]). A calibration exercise for %C 37:4 comparable to those undertaken in the Atlantic using surface sediments has not been performed in the northern Pacific; thus, we do not apply the %C 37:4 proxy as a method of quantifying past SSS or SST.…”

Section: Evaluation Of the Alkenone Proxy Recordsmentioning

confidence: 95%

“…[12] Modern calibration exercises have demonstrated that high %C 37:4 values in both particulate organic matter and surface sediments are associated with low-temperature and low-salinity surface water masses of the Arctic and Polar Water domains [Bendle and Rosell-Melé, 2004;Bendle et al, 2005;Harada et al, 2006;Sicre et al, 2002]. Thus, %C 37:4 in sediments exceeds 5% below Arctic Atlantic Waters (north of the Arctic Front, delineated using the 35 p.s.u.…”

Section: Evaluation Of the Alkenone Proxy Recordsmentioning

confidence: 99%

“…However, the multivariate control over %C 37:4 by salinity and temperature prevents the application of %C 37:4 to quantify past SSS or SSTs [Bendle et al, 2005]. High concentrations of C 37:4 are associated with the cooler and fresher water masses found in the Pacific subarctic [Harada et al, 2006]. The correlation between %C 37:4 and SSS in the Pacific subarctic was strong (R 2 = 0.76), although the relationship was insignificant for %C 37:4 versus SST (R 2 = 0.17; [Bendle et al, 2005;Harada et al, 2006]).…”

Section: Evaluation Of the Alkenone Proxy Recordsmentioning

confidence: 99%

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Expansion of subarctic water masses in the North Atlantic and Pacific oceans and implications for mid‐Pleistocene ice sheet growth

et al. 2008

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[1] Past surface ocean circulation changes associated with the mid-Pleistocene transition, 0.9-0.6 Ma, were reconstructed in the northern North Atlantic (ODP 983) and the northwest Pacific (ODP 882), using proxies for subarctic/subpolar water mass distributions (%C 37:4 alkenone) and sea surface temperature (U 37 K ). Both sites experienced a secular expansion of subarctic waters from $1.15 Ma, spanning both glacial and interglacial intervals. After 0.9 Ma, low %C 37:4 at Site 983 records a northward retreat of subarctic waters during interglacials in the Atlantic, while continued high glacial %C 37:4 indicate extensive subarctic waters during glacial maxima associated with the development of the larger late Pleistocene ice sheets. In contrast, a secular decline in %C 37:4 occurred at Site 882 from 0.9 to 0.5 Ma, marking a more gradual retreat of subarctic conditions in the Pacific. It is proposed that the expansion of subarctic waters between 1.15 and 0.9 Ma exerted negative feedbacks to the moisture supply to the ice sheet source regions and may account for the apparent delayed ice sheet response to atmosphere-ocean circulation changes associated with the mid-Pleistocene transition that began as early as 1.2 Ma.

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Paleoproductivity in the northwestern Pacific Ocean during the Pliocene‐Pleistocene climate transition (3.0–1.8 Ma)

2017

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Alkenone mass accumulation rates (MARs) provide a proxy for export productivity in the northwestern Pacific (Ocean Drilling Program Site 1208) spanning the late Pliocene through early Pleistocene (3.0–1.8 Ma). We investigate changes in productivity associated with global cooling during the onset and expansion of Northern Hemisphere glaciation (NHG). Alkenone MARs vary on obliquity timescales throughout, but the amplitude increases at 2.75 Ma concurrent with the intensification of NHG and cooling of the sea surface by 3°C. The obliquity‐scale variations in alkenone MARs parallel shipboard measurements of sediment color reflectance (%) with higher MARs significantly correlated (>95%) with darker (opal‐rich) intervals. Variations in both lead benthic foraminiferal δ18O values by 1.5–2 kyr suggesting that export productivity may be a contributing factor, rather than a response, to the extent of continental glaciation. The biological pump is therefore a plausible mechanism for transferring atmospheric CO2 into the deep ocean during the onset of NHG and the ensuing obliquity‐dominated climate regime. Obliquity‐scale correlation between productivity and magnetic susceptibility is consistent with a link via westerly winds delivering terrigenous sediments and mixing the upper water column. Alkenone MARs also contain a ~400 kyr modulation. Because this periodicity is a multiple of the residence time of carbon in the ocean, it may reflect inputs of new nutrients associated with eccentricity‐forced changes in the terrestrial biosphere and weathering. We ascribe these findings to interactions between the East Asian winter monsoon and productivity in the North Pacific Ocean, perhaps contributing to Plio‐Pleistocene climate change.

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Characteristics of alkenone distributions in suspended and sinking particles in the northwestern North Pacific

Cited by 44 publications

References 54 publications

Seasonal and depth variations in molecular and isotopic alkenone composition of sinking particles from the western North Pacific

Seasonal and depth variations in molecular and isotopic alkenone composition of sinking particles from the western North Pacific

Expansion of subarctic water masses in the North Atlantic and Pacific oceans and implications for mid‐Pleistocene ice sheet growth

Paleoproductivity in the northwestern Pacific Ocean during the Pliocene‐Pleistocene climate transition (3.0–1.8 Ma)

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