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Glacial‐Holocene δ 15 N record from the Gulf of Tehuantepec, Mexico: Implications for denitrification in the eastern equatorial Pacific and changes in atmospheric N 2 O
Author(s) -
Thunell Robert C.,
Kepple Alisa B.
Publication year - 2004
Publication title -
global biogeochemical cycles
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.512
H-Index - 187
eISSN - 1944-9224
pISSN - 0886-6236
DOI - 10.1029/2002gb002028
Subject(s) - deglaciation , holocene , glacial period , oceanography , last glacial maximum , geology , denitrification , glacier , ice core , sediment , physical geography , nitrogen , geomorphology , chemistry , geography , organic chemistry
The intensity of denitrification in the Gulf of Tehuantepec, along the Mexican margin of the eastern tropical North Pacific (ETNP), was reconstructed for the last 23,000 years using the nitrogen isotopic composition of sediment organic matter (δ 15 N org ) in conjunction with other geochemical tracers of water column productivity. During the last glacial period, δ 15 N org values ranged from 6.5 to 8.6‰ with values increasing between 23 and 17 ka. Deglaciation was marked by an abrupt increase in δ 15 N org with maximum values (9.9‰) occurring during the Bølling/Allerød period and the earliest Holocene. A decline in δ 15 N org values occurred over the last 10,000 years, with late Holocene values being similar to those of the glacial period. Our data suggest that denitrification in this region was minimal during the last glacial and is consistent with the deposition of bioturbated sediments at the study site. The intensity of denitrification increased dramatically during deglaciation and the early Holocene, signaling the presence of a strong oxygen minimum zone. This period is also marked by the deposition of laminated sediments in the region. The δ 15 N org records display similar temporal trends to those seen in the Greenland ice core record of atmospheric N 2 O concentrations. At present, denitrification within the eastern tropical Pacific and Arabian Sea accounts for a major portion of the global marine loss of fixed nitrogen, and a significant fraction of the ocean‐atmosphere N 2 O flux originates from these areas. Large changes in N 2 O emissions from these regions in the past would have directly impacted global greenhouse gas concentrations.