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Rigual-Hernández AS, Sierro FJ, Flores JA, Trull TW, Rodrigues T, Martrat B, Sikes EL, Nodder SD, Eriksen RS, Davies D, Bravo N, Sánchez-Santos JM, Abrantes F. Influence of environmental variability and Emiliania huxleyi ecotypes on alkenone-derived temperature reconstructions in the subantarctic Southern Ocean. THE SCIENCE OF THE TOTAL ENVIRONMENT 2022; 812:152474. [PMID: 34952068 DOI: 10.1016/j.scitotenv.2021.152474] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/12/2021] [Revised: 12/10/2021] [Accepted: 12/13/2021] [Indexed: 06/14/2023]
Abstract
Long-chain unsaturated alkenones produced by haptophyte algae are widely used as paleotemperature indicators. The unsaturation relationship to temperature is linear at mid-latitudes, however, non-linear responses detected in subpolar regions of both hemispheres have suggested complicating factors in these environments. To assess the influence of biotic and abiotic factors in alkenone production and preservation in the Subantarctic Zone, alkenone fluxes were quantified in three vertically-moored sediment traps deployed at the SOTS observatory (140°E, 47°S) during a year. Alkenone fluxes were compared with coccolithophore assemblages, satellite measurements and surface-water properties obtained by sensors at SOTS. Alkenone-based temperature reconstructions generally mirrored the seasonal variations of SSTs, except for late winter when significant deviations were observed (3-10 °C). Annual flux-weighted averages in the 3800 m trap returned alkenone-derived temperatures ~1.5 °C warmer than those derived from the 1000 m trap, a distortion attributed to surface production and signal preservation during its transit through the water column. Notably, changes in the relative abundance of E. huxleyi var. huxleyi were positively correlated with temperature deviations between the alkenone-derived temperatures and in situ SSTs (r = 0.6 and 0.7 at 1000 and 2000 m, respectively), while E. huxleyi var. aurorae, displayed an opposite trend. Our results suggest that E. huxleyi var. aurorae produces a higher proportion of C37:3 relative to C37:2 compared to its counterparts. Therefore, the dominance of var. aurorae south of the Subtropical Front could be at least partially responsible for the less accurate alkenone-based SST reconstructions in the Southern Ocean using global calibrations. However, the observed correlations were largely influenced by the samples collected during winter, a period characterized by low particle fluxes and slow sinking rates. Thus, it is likely that other factors such as selective degradation of the most unsaturated alkenones could also account for the deviations of the alkenone paleothermometer.
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Affiliation(s)
- A S Rigual-Hernández
- Área de Paleontología, Departamento de Geología, Universidad de Salamanca, 37008 Salamanca, Spain.
| | - F J Sierro
- Área de Paleontología, Departamento de Geología, Universidad de Salamanca, 37008 Salamanca, Spain
| | - J A Flores
- Área de Paleontología, Departamento de Geología, Universidad de Salamanca, 37008 Salamanca, Spain
| | - T W Trull
- CSIRO Oceans and Atmosphere, Hobart, Tasmania 7001, Australia; Institute for Marine and Antarctic Studies, University of Tasmania, Private Bag 129, Hobart, Tasmania 7001, Australia; Antarctic Climate and Ecosystems Cooperative Research Centre and Australian Antarctic Program Partnership, University of Tasmania, Hobart, Tasmania 7001, Australia
| | - T Rodrigues
- Portuguese Institute for Sea and Atmosphere (IPMA), Divisão de Geologia Marinha (DivGM), Rua Alfredo Magalhães Ramalho 6, Lisboa, Portugal; CCMAR, Centro de Ciências do Mar, Universidade do Algarve, Campus de Gambelas, 8005-139 Faro, Portugal
| | - B Martrat
- Department of Environmental Chemistry, IDAEA-CSIC, 08034 Barcelona, Spain
| | - E L Sikes
- Marine and Coastal Sciences, Rutgers University, New Brunswick, NJ, USA
| | - S D Nodder
- National Institute of Water and Atmospheric Research, Wellington 6021, New Zealand
| | - R S Eriksen
- CSIRO Oceans and Atmosphere, Hobart, Tasmania 7001, Australia; Institute for Marine and Antarctic Studies, University of Tasmania, Private Bag 129, Hobart, Tasmania 7001, Australia
| | - D Davies
- CSIRO Oceans and Atmosphere, Hobart, Tasmania 7001, Australia; Antarctic Climate and Ecosystems Cooperative Research Centre and Australian Antarctic Program Partnership, University of Tasmania, Hobart, Tasmania 7001, Australia
| | - N Bravo
- Department of Environmental Chemistry, IDAEA-CSIC, 08034 Barcelona, Spain
| | - J M Sánchez-Santos
- Departamento de Estadística, Universidad de Salamanca, 37008 Salamanca, Spain
| | - F Abrantes
- Portuguese Institute for Sea and Atmosphere (IPMA), Divisão de Geologia Marinha (DivGM), Rua Alfredo Magalhães Ramalho 6, Lisboa, Portugal; CCMAR, Centro de Ciências do Mar, Universidade do Algarve, Campus de Gambelas, 8005-139 Faro, Portugal
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Endo H, Hanawa Y, Araie H, Suzuki I, Shiraiwa Y. Overexpression of Tisochrysis lutea Akd1 identifies a key cold-induced alkenone desaturase enzyme. Sci Rep 2018; 8:11230. [PMID: 30046151 PMCID: PMC6060089 DOI: 10.1038/s41598-018-29482-8] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2018] [Accepted: 07/12/2018] [Indexed: 12/28/2022] Open
Abstract
Alkenones are unusual long-chain neutral lipids that were first identified in oceanic sediments. Currently they are regarded as reliable palaeothermometers, since their unsaturation status changes depending on temperature. These molecules are synthesised by specific haptophyte algae and are stored in the lipid body as the main energy storage molecules. However, the molecular mechanisms that regulate the alkenone biosynthetic pathway, especially the low temperature-dependent desaturation reaction, have not been elucidated. Here, using an alkenone-producing haptophyte alga, Tisochrysis lutea, we show that the alkenone desaturation reaction is catalysed by a newly identified desaturase. We first isolated two candidate desaturase genes and found that one of these genes was drastically upregulated in response to cold stress. Gas chromatographic analysis revealed that the overexpression of this gene, named as Akd1 finally, increased the conversion of di-unsaturated C37-alkenone to tri-unsaturated molecule by alkenone desaturation, even at a high temperature when endogenous desaturation is efficiently suppressed. We anticipate that the Akd1 gene will be of great help for elucidating more detailed mechanisms of temperature response of alkenone desaturation, and identification of active species contributing alkenone production in metagenomic and/or metatranscriptomic studies in the field of oceanic biogeochemistry.
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Affiliation(s)
- Hirotoshi Endo
- Faculty of Life and Environmental Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki, 305-8572, Japan
| | - Yutaka Hanawa
- Faculty of Life and Environmental Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki, 305-8572, Japan
| | - Hiroya Araie
- Faculty of Life and Environmental Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki, 305-8572, Japan.,College of Science and Engineering, Kanto Gakuin University, 1-50-1 Mutsuura-higashi, Kanazawa-ku, Yokohama, Kanagawa, 236-8501, Japan
| | - Iwane Suzuki
- Faculty of Life and Environmental Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki, 305-8572, Japan
| | - Yoshihiro Shiraiwa
- Faculty of Life and Environmental Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki, 305-8572, Japan.
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