Salinity of the Eocene Arctic Ocean from oxygen isotope analysis of fish bone carbonate

Abstract

Stable isotope analysis was performed on the structural carbonate of fish bone apatite from early and early middle Eocene samples (∼55 to ∼45 Ma) recently recovered from the Lomonosov Ridge by Integrated Ocean Drilling Program Expedition 302 (the Arctic Coring Expedition). The δ18O values of the Eocene samples ranged from −6.84‰ to −2.96‰ Vienna Peedee belemnite, with a mean value of −4.89‰, compared to 2.77‰ for a Miocene sample in the overlying section. An average salinity of 21 to 25‰ was calculated for the Eocene Arctic, compared to 35‰ for the Miocene, with lower salinities during the Paleocene Eocene thermal maximum, the Azolla event at ∼48.7 Ma, and a third previously unidentified event at ∼47.6 Ma. At the Azolla event, where the organic carbon content of the sediment reaches a maximum, a positive δ13C excursion was observed, indicating unusually high productivity in the surface waters.

Expanding the Cenozoic paleoceanographic record in the Central Arctic Ocean: IODP Expedition 302 Synthesis

“…However in situ generation of oil and gas has not occurred as demonstrated by the immaturity of the ACEX sediments based on Tmax and vitrinite reflectance values [48]. The depositional environment, interpreted from fish remains, suggests low surface water salinities (21-25 ≤) throughout the Eocene [86]. The composition of the biosilica groups, containing largely endemic assemblages of marine diatoms, ebridians, and chrysophyte cysts, is consistent with a strong halocline separating the uppermost near-fresh and/or brackish waters from the underlying waters containing assemblages that require more saline conditions [64] (Figure 9).…”

“…The Amerasian Basin was the only deep basin in the Arctic Ocean for about [80][81][82][83][84][85][86][87][88][89][90] Myr. The Lomonosov Ridge separates the older Amerasian Basin from the younger Eurasian Basin (Figure 1).…”

Paleoenvironmental implications of Cenozoic sediments from the central Arctic Ocean (IODP Expedition 302) using inorganic geochemistry

“…This induced Mn oxide formation, followed by transformation to Mn carbonates in otherwise anoxic sediments with significant enrichments of trace metals indicative for anoxic to euxinic bottom waters [e.g., Huckriede and Meischner, 1996;Emeis et al, 1998;Sternbeck et al, 2000;Sohlenius et al, 2001;Neumann et al, 2002]. Episodic, but short-termed flushing events of the deep Arctic Ocean during Eocene times with saline marine waters from the Atlantic are supported by Nd isotope data from fish bones [Waddell and Moore, 2008;Gleason et al, 2009] and by silicofossil preservation [Stickley et al, 2008]. Also a more detailed look at the records of generally enriched trace elements of Co, Cu, Fe, Mo, Ni, V and Zn reveals considerable variability (Figures 6 and 7) that is probably related to rapid changes in bottom water redox conditions.…”

A model study of the first ventilated regime of the Arctic Ocean during the early Miocene

“…From oxygen isotope analysis of fish bones in the ACEX cores, Waddell & Moore (2008) reconstructed the salinity and the temperature from early Eocene to early Miocene (ca. 55 to ca.…”

“…3 (based on Table 3; Waddell & Moore 2008). Fish bone carbonate extracted from apatite is considered to represent burial conditions at the seafloor rather than the water conditions in which the fish lived, implying that the temperatures and salinities by Waddell & Moore (2008) likely represent the palaeodepth of the Lomonosov Ridge crest. Their analysed early Miocene sample provided a temperature of about 68C and salinity of about 35 psu.…”