By analyzing the ratio of heavy to light oxygen contained in fossil shells of planktonic and bottom dwelling foraminifera (single celled marine organisms) Euler and Ninnemann document natural variations in southeast Pacific ocean temperature and salinity during the first 1300 years (A. D.). The fossil shells are recovered from a unique sedimentary sequence recovered from offshore Chile (Ocean Drilling Program Site 1233). The sediments were accumulating so fast that they provide the first decadally resolved paired records of temperature changes in southeast Pacific surface and intermediate water (ca. 800m depth).
The surface water record reveals high-amplitude variations in ocean properties suggesting ocean temperature could have changed by as much as 3°C in less than a century. Such large natural variability may help explain why ocean temperatures in regions of the Southern Hemisphere have not been in phase with global changes over recent decades.
Intermediate waters
The study also provides the first evidence showing that intermediate ocean properties vary with climate on such short timescales, centuries or less, raising the possibility that they the intermediate ocean could play an important role in Pacific wide climate cycles. Both the timing and the sense of the intermediate ocean changes support previous speculations that the high latitude oceans influence tropical climate and El Nino through an “ocean tunnel” at intermediate depths.
The work reveals that intermediate ocean properties may be a crucial component in modulating, and hence predicting, future climate and ocean nutrient cycling over large areas.