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Distribution and Export of Particulate 3‐Hydroxy Fatty Acids in the Northwestern Pacific Ocean: Implications for Seawater Temperature Reconstructions.

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Title: Distribution and Export of Particulate 3‐Hydroxy Fatty Acids in the Northwestern Pacific Ocean: Implications for Seawater Temperature Reconstructions.
Authors: Pan, Fengmin1,2,3 (AUTHOR), Yuan, Huamao1,2,3,4 (AUTHOR) yuanhuamao@qdio.ac.cn, Song, Jinming1,2,3,4 (AUTHOR) jmsong@qdio.ac.cn, Li, Xuegang1,2,3,4 (AUTHOR), Duan, Liqin1,2,3,4 (AUTHOR)
Source: Journal of Geophysical Research. Oceans. Jun2026, Vol. 131 Issue 6, p1-16. 16p.
Subject Terms: *Fatty acids, *Marine sediment analysis, *Organic compounds, *Ocean, *Paleoceanography, Physiological adaptation
Geographic Terms: North Pacific Ocean
Abstract: Bacterial 3‐hydroxy fatty acids (3‐OH‐FAs) have emerged as promising biomarkers for reconstructing seawater temperatures. However, uncertainties regarding their production and transportation from water column to sediments have hindered accurate interpretation of temperature signals reconstructed by sedimentary 3‐OH‐FAs. Here, we present a comprehensive analysis of particulate 3‐OH‐FAs from two water column profiles and corresponding surface sediments in the Northwestern Pacific Ocean (NWP). Particulate 3‐OH‐FA concentrations ranged from 0.69 to 2.95 μg L−1, peaking in the surface layer coinciding with elevated particulate organic carbon (POC) concentrations and higher temperatures. Seawater temperature was the primary factor controlling 3‐OH‐FA distributions in the water column, supported by its highest variable importance in projection score in the partial least squares analysis. Temperature showed a significant negative correlation with relative abundance of branched homologs, consistent with homeoviscous adaptation. An export model based on depth‐specific molecular index Br13+17% (proportion of branched C13 and C17 homologs) indicated that 3‐OH‐FAs in the study area are primarily exported from the subsurface layer (∼200 m), where production and aggregation/packaging efficiency are optimally coupled. The sedimentary 3‐OH‐FA‐based seawater temperature index RAN13 effectively captured the variability of subsurface seawater temperature, consistent with the export model results. Overall, these findings suggest that 3‐OH‐FAs in deep NWP sediments are mainly sourced from subsurface waters, thereby highlighting their potential as a proxy for subsurface temperature reconstructions in this region. Plain Language Summary: Reconstructing past seawater temperature is essential to understand past ocean changes that ultimately serve to understand future changes. Bacterial membrane lipids known as 3‐hydroxy fatty acids (3‐OH‐FAs), which have potential as novel seawater temperature proxies, were investigated in this study to advance their application in paleoceanographic reconstructions. Our results from the Northwestern Pacific Ocean reveal that the abundance of particulate 3‐OH‐FAs peaks in the surface. Particulate 3‐OH‐FAs are exported primarily from the subsurface layer (∼200 m), the depth at which high 3‐OH‐FA production is well matched by the elevated sinking efficiency of particles. Consistently, sedimentary 3‐OH‐FAs in open‐oceans primarily record temperature variations of the subsurface ocean. These results provide fundamental new insights into the water column sources of marine sedimentary 3‐OH‐FAs and the temperature signals recorded by them. Key Points: Temperature is the main factor shaping 3‐OH‐FA distributions following homeoviscous adaptationParticulate 3‐OH‐FAs are predominantly exported from subsurface layers with an optimal coupling of productivity with sinking efficiencySedimentary 3‐OH‐FAs effectively record subsurface‐ocean temperatures with RAN13 as a potential proxy [ABSTRACT FROM AUTHOR]
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Abstract:Bacterial 3‐hydroxy fatty acids (3‐OH‐FAs) have emerged as promising biomarkers for reconstructing seawater temperatures. However, uncertainties regarding their production and transportation from water column to sediments have hindered accurate interpretation of temperature signals reconstructed by sedimentary 3‐OH‐FAs. Here, we present a comprehensive analysis of particulate 3‐OH‐FAs from two water column profiles and corresponding surface sediments in the Northwestern Pacific Ocean (NWP). Particulate 3‐OH‐FA concentrations ranged from 0.69 to 2.95 μg L−1, peaking in the surface layer coinciding with elevated particulate organic carbon (POC) concentrations and higher temperatures. Seawater temperature was the primary factor controlling 3‐OH‐FA distributions in the water column, supported by its highest variable importance in projection score in the partial least squares analysis. Temperature showed a significant negative correlation with relative abundance of branched homologs, consistent with homeoviscous adaptation. An export model based on depth‐specific molecular index Br13+17% (proportion of branched C13 and C17 homologs) indicated that 3‐OH‐FAs in the study area are primarily exported from the subsurface layer (∼200 m), where production and aggregation/packaging efficiency are optimally coupled. The sedimentary 3‐OH‐FA‐based seawater temperature index RAN13 effectively captured the variability of subsurface seawater temperature, consistent with the export model results. Overall, these findings suggest that 3‐OH‐FAs in deep NWP sediments are mainly sourced from subsurface waters, thereby highlighting their potential as a proxy for subsurface temperature reconstructions in this region. Plain Language Summary: Reconstructing past seawater temperature is essential to understand past ocean changes that ultimately serve to understand future changes. Bacterial membrane lipids known as 3‐hydroxy fatty acids (3‐OH‐FAs), which have potential as novel seawater temperature proxies, were investigated in this study to advance their application in paleoceanographic reconstructions. Our results from the Northwestern Pacific Ocean reveal that the abundance of particulate 3‐OH‐FAs peaks in the surface. Particulate 3‐OH‐FAs are exported primarily from the subsurface layer (∼200 m), the depth at which high 3‐OH‐FA production is well matched by the elevated sinking efficiency of particles. Consistently, sedimentary 3‐OH‐FAs in open‐oceans primarily record temperature variations of the subsurface ocean. These results provide fundamental new insights into the water column sources of marine sedimentary 3‐OH‐FAs and the temperature signals recorded by them. Key Points: Temperature is the main factor shaping 3‐OH‐FA distributions following homeoviscous adaptationParticulate 3‐OH‐FAs are predominantly exported from subsurface layers with an optimal coupling of productivity with sinking efficiencySedimentary 3‐OH‐FAs effectively record subsurface‐ocean temperatures with RAN13 as a potential proxy [ABSTRACT FROM AUTHOR]
ISSN:21699275
DOI:10.1029/2026JC024079