Inorganic carbon addition stimulates snow algae primary productivity

Abstract

Earth has experienced glacial/interglacial oscillations accompanied by changes in atmospheric CO 2 throughout much of its history. Today over 15 million square kilometers of Earth's land surface is covered in ice including glaciers, ice caps, and ice sheets. Glaciers are teeming with life and supraglacial snow and ice surfaces are often darkened by the presence of photoautotrophic snow algae, resulting in accelerated melt due to lowered albedo. Few studies report the productivity of snow algal communities and the parameters which constrain their growth on supraglacial surfaces-key factors for quantifying biologically induced albedo effects (bio-albedo). We demonstrate that snow algae primary productivity is stimulated by the addition of inorganic carbon. Our results indicate a positive feedback between increasing CO 2 and snow algal primary productivity, underscoring the need for robust climate models of past and present glacial/interglacial oscillations to include feedbacks between supraglacial primary productivity, albedo, and atmospheric CO 2 .Earth has experienced intervals of glacial and interglacial periods in its history including Snowball Earth events [1,2]. Today, glaciers and ice sheets are integral to the Earth's climate and hydrological system-they influence regional and global climate, are sensitive to climate change, and are the largest freshwater reservoir on Earth [3,4]. Geologic and geochemical evidence suggest that glacial/interglacial oscillations are coincident with lower atmospheric CO 2 [5] and are exacerbated by lower solar luminosity [6]. For instance, models indicate overcoming high planetary albedo during Snowball Earth events required greenhouse warming caused by the accumulation of high levels of CO 2 from volcanic outgassing accompanied by decreases in silicate weathering [7,8]. Due to human activity, atmospheric CO 2 is now above 400 ppm [9] and from 1999 to 2010, CO 2 was emitted at a rate 100 times as fast as during the last glacial termination [10]. Coincident with increasing CO 2 , average global temperatures have increased (~1°C over the past century) leading to glacial retreat and receding snowpack.Glaciers and ice sheets are a host to diverse ecosystems including supraglacial communities that contribute to local and global biogeochemical cycles [11]. Snow algae (eukaryotic photoautotrophs) are key primary producers on supraglacial habitats in the Arctic, and on glaciers and snowfields throughout the world where they thrive in highirradiation environments [12,13]. To overcome this high irradiance, snow algae produce secondary carotenoids resulting in blooms of red algal biomass [14], which darkens snow and ice surfaces. In Sierra Nevada snowfields, snow algae abundance was negatively correlated to surface albedo [15] and a recent study quantified the role of snow algae communities in snowmelt on an icefield in Alaska [16]. Similarly, in the Arctic, red algal blooms darken the snow/ice surface, lowering surface albedo (by as much as 13% over the melt season) [17] and in...

Distribution and biogeography of Sanguina snow algae: Fine‐scale sequence analyses reveal previously unknown population structure

“…Based on models of snow cover during that period (Hoffman et al, 2017), snow algae potentially covered the majority of Earth's habitable surface area and may have influenced snow melt rates and movements of organic carbon pools (Ganey, Loso, Burgess, & Dial, 2017; Hood, Battin, Fellman, O'Neel, & Spencer, 2015). However, it remains unresolved if contemporary snow algae are as influential to global or local nutrient cycling dynamics (but see Hamilton & Havig, 2020).…”

“…Most snow algal taxa belong to the Chlamydomonadales (Chlorophyta) but they can also be found within the Euglenophyta, Cryptophyta, and Chrysophyta among others, albeit with scant representation (Hoham & Remias, 2020). Snow phycological systems have historically been underexplored, with relatively few active researchers (Hoham, 1980; Hoham & Duval, 2001; Kol, 1968; Weiss, 1983), but recently there has been a renaissance of sorts where global investigations into these algae and associated communities have grown extensively (Anesio, Lutz, Chrismas, & Benning, 2017; Brown & Jumpponen, 2019; Brown, Olson, & Jumpponen, 2015; Brown, Ungerer, & Jumpponen, 2016; Davey et al., 2019; Hamilton & Havig, 2017, 2020; Krug, Erlacher, Markut, Berg, & Cernava, 2020; Lutz et al., 2016; Lutz, McCutcheon, McQuaid, & Benning, 2018; Lutz, Prochazkova, Benning, Nedbalova, & Remias, 2019; Müller, Bleiss, Martin, Rogaschewski, & Fuhr, 1998; Procházková, Leya, Křížková, & Nedbalová, 2019; Procházková, Remias, Řezanka, & Nedbalová, 2018; Remias, Procházková, Holzinger, & Nedbalová, 2018; Remias, Procházková, Nedbalová, Andersen, & Valentin, 2020; Segawa et al., 2018; Takeuchi, 2013; Yoshimura, Kohshima, & Ohtani, 1997). While snow algae are diverse, perhaps the most well known are algae that form red blooms in late season open field snows caused by the recently established genus Sanguina (Procházková et al, 2019) [previously assigned to Chlamydomonas cf.…”

Anoxygenic Phototrophs Span Geochemical Gradients and Diverse Morphologies in Terrestrial Geothermal Springs

“…Sulfide, Fe 2+ , and dissolved silica were measured onsite using a DR1900 portable spectrophotometer (Hach Company, Loveland, CO). Water samples were filtered through 0.2-μm polyethersulfone syringe filters (VWR International, Radnor, PA, USA) and analyzed for cation concentration (Na, K, Ca, and Mg), anion concentration (Cl − and SO 4 2− ), trace element concentration (P, Mn, Fe, As, and Mo), dissolved inorganic carbon (DIC) concentration and δ 13 C value, and dissolved organic carbon concentration and δ 13 C value, as described previously (101–103). Field blanks comprised of filtered 18.2 MΩ/cm deionized water, transported to the field in 1-liter Nalgene bottles (acid washed as described above), were collected onsite using the equipment and techniques described above.…”

Ecological Stoichiometry of the Mountain Cryosphere

“…Warming temperatures, and altered precipitation regimes (e.g., more winter precipitation falling as rain rather than snow, Knowles et al, 2006), will directly influence the supraglacial zone and lead to declines in glacier volume, shorter periods of seasonal snow cover, and increased outflows in the near-term that will dwindle as ice sources fade (Huss and Hock, 2018). A longer "growing season" for microbial communities in the supraglacial zone paired with rising atmospheric CO 2 , which will stimulate snow algae growth (Hamilton and Havig, 2018; Figure 1), may yield a concurrent increase in autochthonous organic C production by primary producers (e.g., algae and cyanobacteria). Such a rise in primary production is likely to escalate existing glacial-melt feedback loop by decreasing surface ice albedo (e.g., Ganey et al, 2017).…”

“…The availability and mass balance of key elements [carbon (C), nitrogen (N), and phosphorous (P)] place crucial controls on the population dynamics of organisms (Cross et al, 2005), ultimately regulating the structure, function, and processes of ecosystems (Sterner and Elser, 2002;Elser et al, 2007). On mountain glaciers and snowfields, solar radiation, atmospheric CO 2 , allochthonous (e.g., arthropod fallout, Edwards, 1987;black carbon, Skiles et al, 2018), and autochthonous (e.g., cryoconite hole metabolism, Anesio et al, 2009; snow algae primary productivity, Hamilton and Havig, 2018) inputs all interact to shape elemental balances and the structure of food webs. Furthermore, glacier environments support higher trophic levels (Tynen, 1970;Kohshima, 1984;De Smet and Van Rompu, 1994;Kikuchi, 1994), highlighting the key role that stoichiometric dynamics likely play in shaping ice-associated food webs.…”