Under‐Ice Phytoplankton Blooms Inhibited by Spring Convective Mixing in Refreezing Leads. Issue 1 (7th January 2018)

• Record Type: Journal Article
• Authors: Lowry, Kate E.; Pickart, Robert S.; Selz, Virginia; Mills, Matthew M.; Pacini, Astrid; Lewis, Kate M.; Joy‐Warren, Hannah L.; Nobre, Carolina; van Dijken, Gert L.; Grondin, Pierre‐Luc; Ferland, Joannie; Arrigo, Kevin R.
• Is Part Of: Journal of geophysical research. Volume 123:Issue 1(2018)
• Page Start: 90
• Page End: 109
• Publication Date: 2018-01-07
• Subjects: phytoplankton -- under‐ice blooms -- leads -- convective mixing -- Arctic -- sea ice; Oceanography -- Periodicals; 551.4605
• DOI: 10.1002/2016JC012575
• Languages: English
• ISSNs: 2169-9275

Abstract

Abstract: Spring phytoplankton growth in polar marine ecosystems is limited by light availability beneath ice‐covered waters, particularly early in the season prior to snowmelt and melt pond formation. Leads of open water increase light transmission to the ice‐covered ocean and are sites of air‐sea exchange. We explore the role of leads in controlling phytoplankton bloom dynamics within the sea ice zone of the Arctic Ocean. Data are presented from spring measurements in the Chukchi Sea during the Study of Under‐ice Blooms In the Chukchi Ecosystem (SUBICE) program in May and June 2014. We observed that fully consolidated sea ice supported modest under‐ice blooms, while waters beneath sea ice with leads had significantly lower phytoplankton biomass, despite high nutrient availability. Through an analysis of hydrographic and biological properties, we attribute this counterintuitive finding to springtime convective mixing in refreezing leads of open water. Our results demonstrate that waters beneath loosely consolidated sea ice (84–95% ice concentration) had weak stratification and were frequently mixed below the critical depth (the depth at which depth‐integrated production balances depth‐integrated respiration). These findings are supported by theoretical model calculations of under‐ice light, primary production, and critical depth at varied lead fractions. The model demonstrates that under‐ice blooms can form even beneath snow‐covered sea ice in the absence of mixing but not in more deeply mixed waters beneath sea ice with refreezing leads. Future estimates of primary production should account for these phytoplankton dynamics in ice‐covered waters. Key Points: Spring phytoplankton blooms were present beneath fully consolidated sea ice with snow Under‐ice phytoplankton biomass was inversely correlated with lead fraction Convection in refreezing leads enhances mixing and inhibits under‐ice bloom development