Japan Geoscience Union Meeting 2014

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International Session (Oral)

Symbol B (Biogeosciences) » B-PT Paleontology

[B-PT02_1AM2] Biocalcification and the Geochemistry of Proxies

Thu. May 1, 2014 11:00 AM - 12:45 PM 421 (4F)

Convener:*Takashi Toyofuku(Institute of Biogeosciences (BioGeos), Japan Agency for Marine-Earth Science and Technology), Hiroshi Kitazato(Institute of Biogeosciences (BioGeos),Japan Agency for Marine-Earth Science and Technology (JAMSTEC)), Jelle Bijma(Alfred-Wegener-Institut fur Polar- und Meeresforschung), Chair:Takashi Toyofuku(Institute of Biogeosciences (BioGeos), Japan Agency for Marine-Earth Science and Technology)

12:15 PM - 12:30 PM

[BPT02-12] Variation of North Atlantic nitrogen fixation in Caribbean coral skeletons

*Atsuko YAMAZAKI1, Steffen HETZINGER2, Jonas V. REUMONT2, Carrie MANFRINO3, Urumu TSUNOGAI4, Tsuyoshi WATANABE5 (1.AORI, The University of Tokyo, 2.GEOMAR Helmholtz-Zentrum fur Ozeanforschung Kiel, 3.Central Caribbean Marine Institute, 4.Graduate School of Environmental Studies, Nagoya University, 5.Faculty of Science, Hokkaido University)

Keywords:Coral skeletons, nitrogen isotopes, nitrogen fixation, Caribbean Sea, North Atlantic Ocean

Oceanic nitrogen fixation is important as new nitrogen in oligotrophic oceans and balances with denitrification in global nitrogen cycle controlling primary production. North Atlantic ocean is known to have higher nitrogen fixation rates, although the controlling factors have been debated by modern observations and sediment cores in geological time scales. Reef corals have been widely used as paleo-environmental proxy in oligotrophic oceans. Recent studies suggested that nitrogen isotopes of organic matter preserved in coral skeletons δ15Ncoral have the potential to record coral nitrogen sources on decadal to millennia scale. In this study, we report recent 90-year records of nitrogen isotopes in Diploria sp. coral cores from Cayman Islands. δ15Ncoral values were +1.9±2.6 (σ)‰ (n=139), which suggested that the variation of δ15Ncoral was controlled by nitrogen fixation (~0‰) in ambient seawater. The trend line of δ15Ncoral increased ~4‰ from 1920s to 2010s. This result suggests that nitrogen fixation rate in Caribbean Sea decreased during the past 90 years. Detrended δ15Ncoral showed a negative correlation between Atlantic Multi-decadal Oscillation (AMO) index (R=-0.71, P‹‹0.001), which suggested that nitrogen fixation rate increased in higher SST condition leading an index for hurricane activity on multi-decadal scales. In this presentation, we discuss the relationship between nitrogen fixation and hurricane activity in global warming state.