Paleoecological significance of laminated diatomaceous oozes during the middle-to-late Pleistocene, North Atlantic Ocean (IODP Site U1304)

Insights into nitrogen cycling in the western Gulf of California from the nitrogen isotopic composition of diatom-bound organic matter

“…Second, the correlation indicates that deep dwelling diatoms using nitrogen from the nitracline may represent a significant source of export production that is not associated with the winter upwelling season. The correlation between values of δ 15 N large and δ 15 N bulk provides support of previous work, which suggests large diatoms, such as T. longissima , increase export production [ Kemp et al , 2000; Pike and Kemp , 1997; Sancetta et al , 1991; Shimada et al , 2008]. A first order approximation of the total nitrogen exported to the sediment by the large diatoms is 3–15% of total N in the bulk sediment.…”

The intensification of northern component deepwater formation during the mid‐Pleistocene climate transition

“…The deepwater circulation change observed at Site 1063 during MIS 18 and MIS 17 is consistent with the timing of surface ocean hydrographic changes in the North Atlantic. Studies from North Atlantic sites have argued for a shift in the position of the interglacial Arctic Front (AF) during the MPT [ Wright and Flower , ; Shimada et al ., ; McClymont et al ., ; Hernandez‐Almeida et al ., ]. The AF refers to the complex mixing zone separating cold (less saline) surface waters exiting the Arctic Ocean through the Fram Strait on the western side of the basin from the warmer (more saline) surface waters entering the NGS through the North Atlantic Current (NAC) on the eastern side of the basin [ Swift and Aagaard , ; Johannessen et al ., ].…”

Morphological and phylogenetic comparisons ofNeodenticula seminae(Bacillariophyta) populations between the subarctic Pacific and the Gulf of St. Lawrence

“…The latter is usually reported from Antarctica, but was recently observed in the Bering Sea (Kang et al, 1996). N. seminae had been extinct from the North Atlantic phytoplankton since the late Quaternary (0.84 Ma) (Koc¸& Flower, 1998;Koc¸et al, 1999;Shimada et al, 2008). It was recorded from high latitudes of the North Atlantic from Neogene and Quaternary sediments, and was associated with the presence of cool, low salinity surface water (Baldauf, 1984(Baldauf, , 1986.…”

“…This pelagic diatom was considered indicative of an influx of colder polar water into the North Atlantic (Baldauf, 1984(Baldauf, , 1986, and it was postulated that an ice-free polar connection may have existed between the North Atlantic and the Bering Sea during the middle Quaternary (Baldauf, 1987). Recently, Koc¸et al (1999) interpreted the first occurrence of N. seminae in the North Atlantic as a sign of cooling, starting 1.26 Ma, leading to the establishment of 100 000-year cycles with severe glacial periods (Shimada et al, 2008). N. seminae has never been reported from surface sediments in the Canadian High Arctic (Williams, 1986;Kravitz et al, 1987;Campeau et al, 1999Campeau et al, , 2000De Se`ve, 1999).…”

“…N. seminae has been also reported as flourishing in the North Atlantic from the Late Pliocene to Late Pleistocene, roughly 3.3 to 0.8 Ma (Koc¸& Flower, 1998). A high-resolution study of Pleistocene diatom stratigraphy revealed that the first and last occurrences of N. seminae within the Quaternary were 1.26 and 0.84 Ma (Koc¸et al, 1999), indicating that it has been extinct in the North Atlantic since then (Baldauf, 1984;Koc¸et al, 1999;Shimada et al, 2008).…”