Phytoplankton and dimethylsulfide dynamics at two contrasting Arctic ice edges

Abstract

Abstract. Arctic sea ice is retreating and thinning and its rate of decline has steepened in the last decades. While phytoplankton blooms are known to seasonally propagate along the ice edge as it recedes from spring to summer, the substitution of thick multiyear ice (MYI) with thinner, ponded first-year ice (FYI) represents an unequal exchange when considering the roles sea ice plays in the ecology and climate of the Arctic. Consequences of this shifting sea ice on the phenology of phytoplankton and the associated cycling of the climate-relevant gas dimethylsulfide (DMS) and its precursor dimethylsulfoniopropionate (DMSP) remain ill constrained. In July–August 2014, two contrasting ice edges in the Canadian High Arctic were explored: a FYI-dominated ice edge in Barrow Strait and a MYI-dominated ice edge in Nares Strait. Our results reveal two distinct planktonic systems and associated DMS dynamics in connection to these diverging ice types. The surface waters exiting the ponded FYI in Barrow Strait were characterized by moderate chlorophyll a (Chl a, <2.1 µg L−1) as well as high DMSP (115 nmol L−1) and DMS (12 nmol L−1), suggesting that a bloom had already started to develop under the markedly melt-pond-covered (ca. 40 %) FYI. Heightened DMS concentrations at the FYI edge were strongly related to ice-associated seeding of DMS in surface waters and haline-driven stratification linked to ice melt (Spearman's rank correlation between DMS and salinity, rs=-0.91, p<0.001, n=20). However, surface waters exiting the MYI edge at the head of Nares Strait were characterized by low concentrations of Chl a (<0.5 µg L−1), DMSP (<16 nmol L−1), and DMS (<0.4 nmol L−1), despite the nutrient-replete conditions characterizing the surface waters. The increase in autotrophic biomass and methylated sulfur compounds took place several kilometers (ca. 100 km) away from the MYI edge, suggesting the requisite for ice-free, light-sufficient conditions for a phytoplankton bloom to fully develop and for sulfur compound dynamics to follow and expand. In light of the ongoing and projected climate-driven changes to Arctic sea ice, results from this study suggest that the early onset of autotrophic blooms under thinner, melt-pond-covered ice may have vast implications for the timing and magnitude of DMS pulses in the Arctic.

DMS emissions from the Arctic marginal ice zone

“…The distribution of DMSP t and DMS across the Baffin Bay receding ice edge largely followed the evolution of the phytoplankton bloom. The maximum observed DMSP t (524 nM) and DMS (74 nM) concentrations are, by far, the highest reported in the Atlantic and Canadian sectors of the Arctic to our knowledge (see compilations by Jarníková et al, 2018, andMatrai et al, 2007;Lizotte et al, 2020). Observed near-surface DMS concentrations and sea-air F DMS were within the range of previous studies (Table 3).…”

“…Studies in undersampled regions (Central Basin and Siberian shelves, e.g., Uhlig et al, 2019;Schanke et al, 2020) are needed to upscale in situ measurements and generalize current knowledge. The transition toward a first-year Arctic ice cap may favor a high-DMS MIZ such as the one described here in contrast to the low DMS concentrations associated with multi-year ice margins (Lizotte et al, 2020).…”

“…At both laboratories, DMSP was analyzed as DMS after stoichiometric base (NaOH) cleavage. At UL, the evolved DMS was analyzed in a GC-MS (GC: Agilent Intuvo 9000; MS: Agilent 5977B), and peak areas determined with the Mas-sHunter software were converted to concentration against a 7-point calibration of a diluted DMSP standard solution (R 2 > 0.99; Lizotte et al, 2020). At SUNY-ESF, DMSP was quantified following the procedure outlined in on a Shimadzu GC-14A with flame photometric detector.…”

“…The multiple biogeochemical pathways that mediate between DMSP synthesis and DMS emission generally tend to buffer DMS concentrations in open ocean settings (Galí and Simó, 2015), where sea-surface DMS concentrations above 10 nM are rare (Lana et al, 2011). In the MIZ, however, seawater DMS concentrations and sea-air DMS fluxes (F DMS ) can greatly increase when some factors cooccur, namely: the formation of massive phytoplankton blooms (Perrette et al, 2011;Arrigo et al, 2014;Renaut et al, 2018) depending on the type of ice edge (multi-year versus first-year sea ice; Lizotte et al, 2020); the presence of high DMSP and DMS producers (Levasseur, 2013); the enhancement of DMS production by food-web interactions or physiological stress (Matrai et al, 1995;Sunda et al, 2007;Galí et al, 2013); and weak biological DMS removal during early bloom stages (del Valle et al, 2009). Among these factors, blooms of the colony-forming haptophyte Phaeocystis are thought to play a prominent role.…”

Spatiotemporal Variability in Modeled Bottom Ice and Sea Surface Dimethylsulfide Concentrations and Fluxes in the Arctic During 1979–2015

“…Our results indicate higher spatial variability in these products than the in situ measurement-based climatology. The claim for higher variability is supported by the data collected from recent field campaigns (Abbatt et al, 2019;Jarnkov et al, 2018;Lizotte et al, 2020). These data can improve the quality of the Arctic DMS climatology by increasing the data coverage, as these field campaigns focused on regions lacking data in the L11 climatology, such as the Canadian Polar Shelf during July-August.…”