Upper Ocean Biogeochemistry of the Oligotrophic North Pacific Subtropical Gyre: From Nutrient Sources to Carbon Export

Minhan Dai, Ya Wei Luo, Eric P. Achterberg, Thomas J. Browning, Yihua Cai, Zhimian Cao, Fei Chai, Bingzhang Chen, Matthew J. Church, Dongjian Ci, Chuanjun Du, Kunshan Gao, Xianghui Guo, Zhendong Hu, Shuh Ji Kao, Edward A. Laws, Zhongping Lee, Hongyang Lin, Qian Liu, Xin LiuWeicheng Luo, Feifei Meng, Shaoling Shang, Dalin Shi, Hiroaki Saito, Luping Song, Xianhui Sean Wan, Yuntao Wang, Wei Lei Wang, Zuozhu Wen, Peng Xiu, Jing Zhang, Ruifeng Zhang, Kuanbo Zhou

Research output: Contribution to journalReview articlepeer-review

10 Scopus citations

Abstract

Subtropical gyres cover 26%–29% of the world's surface ocean and are conventionally regarded as ocean deserts due to their permanent stratification, depleted surface nutrients, and low biological productivity. Despite tremendous advances over the past three decades, particularly through the Hawaii Ocean Time-series and the Bermuda Atlantic Time-series Study, which have revolutionized our understanding of the biogeochemistry in oligotrophic marine ecosystems, the gyres remain understudied. We review current understanding of upper ocean biogeochemistry in the North Pacific Subtropical Gyre, considering other subtropical gyres for comparison. We focus our synthesis on spatial variability, which shows larger than expected dynamic ranges of properties such as nutrient concentrations, rates of N2 fixation, and biological production. This review provides new insights into how nutrient sources drive community structure and export in upper subtropical gyres. We examine the euphotic zone (EZ) in subtropical gyres as a two-layered vertically structured system: a nutrient-depleted layer above the top of the nutricline in the well-lit upper ocean and a nutrient-replete layer below in the dimly lit waters. These layers vary in nutrient supply and stoichiometries and physical forcing, promoting differences in community structure and food webs, with direct impacts on the magnitude and composition of export production. We evaluate long-term variations in key biogeochemical parameters in both of these EZ layers. Finally, we identify major knowledge gaps and research challenges in these vast and unique systems that offer opportunities for future studies.

Original languageEnglish
Article numbere2022RG000800
JournalReviews of Geophysics
Volume61
Issue number3
DOIs
StatePublished - Sep 2023

Keywords

  • North Pacific Subtropical Gyres
  • biogeochemistry
  • euphotic zone
  • export production
  • nutrient-depleted layer
  • nutrient-replete layer
  • nutrients
  • oligotrophic ocean
  • subtropical gyres

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