Open AccessInterhemispheric leakage of isotopically heavy nitrate in the eastern tropical Pacific during the last glacial period
Author(s) -
Pichevin Laetitia E.,
Ganeshram Raja S.,
Francavilla Stephen,
ArellanoTorres Elsa,
Pedersen Tom F.,
Beaufort Luc
Publication year - 2010
Publication title -
paleoceanography
Language(s) - English
Resource type - Journals
eISSN - 1944-9186
pISSN - 0883-8305
DOI - 10.1029/2009pa001754
Subject(s) - denitrification , oceanography , northern hemisphere , geology , nitrate , southern hemisphere , glacial period , subtropics , ice core , period (music) , climatology , environmental science , nitrogen , paleontology , ecology , physics , quantum mechanics , acoustics , biology
We present new high‐resolution N isotope records from the Gulf of Tehuantepec and the Nicaragua Basin spanning the last 50–70 ka. The Tehuantepec site is situated within the core of the north subtropical denitrification zone while the Nicaragua site is at the southern boundary. The δ 15 N record from Nicaragua shows an “Antarctic” timing similar to denitrification changes observed off Peru‐Chile but is radically different from the northern records. We attribute this to the leakage of isotopically heavy nitrate from the South Pacific oxygen minimum zone (OMZ) into the Nicaragua Basin. The Nicaragua record leads the other eastern tropical North Pacific (ETNP) records by about 1000 years because denitrification peaks in the eastern tropical South Pacific (ETSP) before denitrification starts to increase in the Northern Hemisphere OMZ, i.e., during warming episodes in Antarctica. We find that the influence of the heavy nitrate leakage from the ETSP is still noticeable, although attenuated, in the Gulf of Tehuantepec record, particularly at the end of the Heinrich events, and tends to alter the recording of millennial timescale denitrification changes in the ETNP. This implies (1) that sedimentary δ 15 N records from the southern parts of the ETNP cannot be used straightforwardly as a proxy for local denitrification and (2) that denitrification history in the ETNP, like in the Arabian Sea, is synchronous with Greenland temperature changes. These observations reinforce the conclusion that on millennial timescales during the last ice age, denitrification in the ETNP is strongly influenced by climatic variations that originated in the high‐latitude North Atlantic region, while commensurate changes in Southern Ocean hydrography more directly, and slightly earlier, affected oxygen concentrations in the ETSP. Furthermore, the δ 15 N records imply ongoing physical communication across the equator in the shallow subsurface continuously over the last 50–70 ka.