Estimates of micro-, nano-, and picoplankton contributions to particle export in the northeast Pacific

Abstract

Abstract. The contributions of micro-, nano-, and picoplankton to particle export were estimated from measurements of size-fractionated particulate 234 Th, organic carbon, and phytoplankton indicator pigments obtained during five cruises between 2010 and 2012 along Line P in the subarctic northeast Pacific Ocean. Sinking fluxes of particulate organic carbon (POC) and indicator pigments were calculated from 234 Th-238 U disequilibria and, during two cruises, measured by a sediment trap at Ocean Station Papa. POC fluxes at 100 m ranged from 0.65 to 7.95 mmol m −2 d −1 , similar in magnitude to previous results at Line P. Microplankton pigments dominate indicator pigment fluxes (averaging 69 ± 19 % of total pigment flux), while nanoplankton pigments comprised the majority of pigment standing stocks (averaging 64 ± 23 % of total pigment standing stocks). Indicator pigment loss rates (the ratio of pigment export flux to pigment standing stocks) point to preferential export of larger microplankton relative to smaller nano-and picoplankton. However, indicator pigments do not quantitatively trace particle export resulting from zooplankton grazing, which may be an important pathway for the export of small phytoplankton. These results have important implications for understanding the magnitude and mechanisms controlling the biological pump at Line P in particular, and more generally in oligotrophic gyres and high-nutrient, low-chlorophyll (HNLC) regions where small phytoplankton represent a major component of the autotrophic community.

Carbon export fluxes and export efficiency in the central Arctic during the record sea‐ice minimum in 2012: a joint 234Th/238U and 210Po/210Pb study

“…as its major constituent. Our finding is in line with recent observations that reveal that small cells are important contributors to POC export fluxes in diverse oceanic regimes [e.g., Richardson and Jackson , ; Lomas and Moran , ; Durkin et al ., ; Mackinson et al ., ; Puigcorbé et al ., ]. Prasinophytes, including Micromonas spp., are common in the central Arctic [ Booth and Horner , ; Sherr et al ., ; Zhang et al ., ], and are considered to be among the most abundant photosynthetic cells in pan‐Arctic waters [ Lovejoy et al ., ].…”

“…We encourage future studies applying radionuclide proxies to consider NSS conditions and follow the trend of C/Th and C/Po ratios with time to better constrain the POC fluxes in the Arctic. Further, the simultaneous use of sediment traps would allow the determination of the particle flux composition, which has been pointed out as a crucial factor shaping the biological pump efficiency [e.g., Mackinson et al, 2015;Puigcorb e et al, 2016;Roca-Mart ı et al, 2016].…”

Phytoplankton size impact on export flux in the global ocean

“…In our case, this would be equivalent to p ze × (1 − α ), which is 2% when large cells dominate. Our results add weight to the growing body of literature underscoring the importance of picoplankton contribution to POC flux both at time series locations and throughout the ocean in general [ Brew et al ., ; Lomas and Moran , ; Mackinson et al ., ; Richardson and Jackson , ].…”

“…The phytoplankton community at OSP had a mean S fm of 18%, lower than both K2 and CARIACO (Figure ), although net annual production is almost identical to K2. OSP is located in the northeast Pacific Ocean in the southern part of the Alaska Gyre in a high‐nutrient low‐chlorophyll (HNLC) region that is iron limited [ Mackinson et al ., ; Timothy et al ., ; Wong et al ., ]. Diatoms, coccolithophores, and foraminifera contribute significantly to POC flux at OSP, although there is a large interannual variability in species composition related to ENSO events [ Timothy et al ., ; Wong et al ., ].…”

Phytoplankton Community Structure Is Driven by Stratification in the Oligotrophic Mediterranean Sea

“…Cell size affects nutrient uptake, i.e., smaller cells have an advantage over larger cells for nutrient acquisition in nutrient-depleted environments as a consequence of their higher surface-area-to-volume ratio (Marañón et al, 2012). Sinking and grazing rates are also size-dependent as larger cells sink more efficiently (Mackinson et al, 2015) and faster (Marañón, 2015) than smaller phytoplankton cells. It has been argued that larger phytoplankton cells can escape grazing more easily than smaller cells due to the different generation times of their main predators, metazoans and protists, respectively (Acevedo-Trejos et al, 2015; Marañón, 2015 and references therein).…”