Long-chain diols in settling particles in tropical oceans: insights into sources, seasonality and proxies

• Published in: Biogeosciences Vol. 16; no. 8; pp. 1705 - 1727
• Main Authors: de Bar, Marijke W, Ullgren, Jenny E, Thunnell, Robert C, Wakeham, Stuart G, Brummer, Geert-Jan A, Stuut, Jan-Berend W, Sinninghe Damsté, Jaap S, Schouten, Stefan
• Format: Journal Article
• Language: English
• Published: Katlenburg-Lindau Copernicus GmbH 25-04-2019; Copernicus Publications
• Subjects: Chains; Density stratification; Diols; Fluxes; Glycols (Class of compounds); Lipids; Liquid crystal displays; Migration; Natural history; Ocean circulation; Ocean currents; Ocean temperature; Oceans; Proxies; Proxy; Satellites; Sea surface; Sea surface temperature; Seasonal variation; Seasonal variations; Seasonality; Sediment; Sediment traps; Sediments; Sediments (Geology); Settling; Stratification; Surface temperature; Temperature; Traps; Tropical climate; Upwelling; Water circulation; Water column; Winds; Mozambique
• ISSN: 1726-4189; 1726-4170; 1726-4189
• DOI: 10.5194/bg-16-1705-2019

In this study we analyzed sediment trap time series from five tropical sites
to assess seasonal variations in concentrations and fluxes of long-chain
diols (LCDs) and associated proxies with emphasis on the long-chain diol
index (LDI) temperature proxy. For the tropical Atlantic, we observe that
generally less than 2 % of LCDs settling from the water column are
preserved in the sediment. The Atlantic and Mozambique Channel traps reveal
minimal seasonal variations in the LDI, similar to the two other lipid-based
temperature proxies TEX86 and U37K′. In addition,
annual mean LDI-derived temperatures are in good agreement with the annual
mean satellite-derived sea surface temperatures (SSTs). In contrast, the LDI
in the Cariaco Basin shows larger seasonal variation, as do the TEX86
and U37K′. Here, the LDI underestimates SST during the
warmest months, which is possibly due to summer stratification and the
habitat depth of the diol producers deepening to around 20–30 m. Surface
sediment LDI temperatures in the Atlantic and Mozambique Channel compare well
with the average LDI-derived temperatures from the overlying sediment traps,
as well as with decadal annual mean SST. Lastly, we observed large seasonal
variations in the diol index, as an indicator of upwelling conditions, at
three sites: in the eastern Atlantic, potentially linked to Guinea Dome
upwelling; in the Cariaco Basin, likely caused by seasonal upwelling; and in
the Mozambique Channel, where diol index variations may be driven by
upwelling from favorable winds and/or eddy migration.