Photic zone changes in the north-west Pacific Ocean from MIS 4–5e
Unknown, Article, Other literature type
Swann, G. E. A.
Snelling, A. M.
- Publisher: European Geosciences Union
(issn: 1814-9332, eissn: 1814-9332)
In comparison to other sectors of the marine system, the palaeoceanography of the subarctic North
Pacific Ocean is poorly constrained. New diatom isotope records of δ<sup>13</sup>C,
δ<sup>18</sup>O, δ<sup>30</sup>Si (δ<sup>13</sup>C<sub>diatom</sub>,
δ<sup>18</sup>O<sub>diatom</sub>, and δ<sup>30</sup>Si<sub>diatom</sub>) are presented alongside existing
geochemical and isotope records to document changes in photic zone conditions, including nutrient
supply and the efficiency of the soft-tissue biological pump, between Marine Isotope Stage (MIS) 4
and MIS 5e. Peaks in opal productivity in MIS 5b/c and MIS 5e are both associated with the
breakdown of the regional halocline stratification and increased nutrient supply to the photic
zone. Whereas the MIS 5e peak is associated with low rates of nutrient utilisation, the MIS 5b/c
peak is associated with significantly higher rates of nutrient utilisation. Both peaks, together
with other smaller increases in productivity in MIS 4 and 5a, culminate with a significant increase
in freshwater input which strengthens/re-establishes the halocline and limits further upwelling of
sub-surface waters to the photic zone. Whilst δ<sup>30</sup>Si<sub>diatom</sub> and previously
published records of diatom δ<sup>15</sup>N (δ<sup>15</sup>N<sub>diatom</sub>)
(Brunelle et al., 2007, 2010) show similar trends until the latter half of MIS 5a, the records
become anti-correlated after this juncture and into MIS 4, suggesting a possible change in photic
zone state such as may occur with a shift to iron or silicon limitation.