Yujeong Lim Marine Ecology Laboratory Spatial and temporal variation of net community production and its regulating factors in the Amundsen Sea, Antarctica Doshik Hahm, Tae Siek Rhee, Hae-Cheol Kim, Jisoo Park, Young-Nam Kim, Hyoung Chul Shin, and SangHoon Lee Yujeong Lim Marine Ecology Laboratory

Introduction Primary Production in the Southern Ocean HNLC (High Nutrient Low Chlorophyll) concentrations Fe limitation [Boyd et al., 2000; Cassar et al., 2007] Antarctic continental shelf seas various Fe sources e.g., seafloor sediments, sea ice, glacial melting [Sedwick and DiTullio, 1997; Coale et al., 2005; Gerringa et al., 2012] Coastal polynyas : 65% of the total primary production Amundsen Sea Polynya (ASP) Pine Island Bay Polynya (PIBP) [Arrigo and van Dijken, 2003] http://earthobservatory.nasa.gov/Features/Polynyas/

Introduction Measurements of ∆ 𝑶 𝟐 /𝐀𝐫 and NCP High-frequency measurements of ∆ 𝑂 2 /𝐴𝑟 using mass spectrometry [Tortell, 2005; Cassar et al., 2009] Net Community Production (NCP) = net primary production – heterotrophic respiration NCP is a measure of the net amount of carbon removed from the atmosphere via this biological pump primary production, environmental parameters [Stanley et al., 2010] NEP = GPP – respiration NPP = GPP – (autotrophs’ own rate of respiration) Net Ecosystem Production http://www.nature.com/scitable/knowledge/library/the-biological-productivity-of-the-ocean-70631104

Introduction Objectives to map the spatial and temporal NCP variations in the Amundsen Sea to identify the NCP regulating factors to better understand the mechanisms controlling the phytoplankton bloom magnitude and timing in the polynyas of the Amundsen Sea

Introduction Two Expeditions Araon, Korean icebreaker Fe limitation Red line 30 December 2010 ~8 January 2011 Green line 9 February 2012 ~6 March 2012 http://earthobservatory.nasa.gov/Features/Polynyas/

(respiration, photosynthesis) Method NCP from 𝑶 𝟐 /𝑨𝒓 Measurements Dissolved oxygen concentration in the mixed layer Biological processes (respiration, photosynthesis) Physical processes (dissolution of air, bubble injection, changes in water temperature and air pressure) + Ar and 𝑂 2 have similar solubilities and diffusivities Ar : biologically inert biologically derived 𝑂 2 [Craig and Hayward, 1987; Cassar et al., 2009] Equilibrator inlet mass spectrometry system (EIMS) [Cassar et al., 2009] Quadrupole mass spectrometer [Cassar et al., 2009]

characteristic mixed layer Method NCP from 𝑶 𝟐 /𝑨𝒓 Measurements Biological oxygen supersaturation prior wind speeds weighted gas transfer velocity =average during 60 days [Reuer et al., 2007, eqution (6)] : the ratio of 𝑂 2 /𝐴𝑟 in the sampled water : the ratio of 𝑂 2 /𝐴𝑟 in the air-saturated water Net primary production unit : [Kaiser et al., 2005] characteristic mixed layer gas exchange time (thickness, velocity) : 𝑂 2 gas transfer velocity : surface water density : saturated concentration 20 days in ASP

Method Ancillary Measurements Sea surface temperature Salinity Chlorophyll-a ~Fluorescence Sea ice concentration ~AMSR-E and SSM/I Mixed layer depths Euphotic depths (1% of the surface irradiance) Fe availability ~variable fluorescence to maximum fluorescence ratio Thermosalinograph (SBE45) [Spreen et al., 2008] [Rintoul and Trull, 2001] Vertical CTD (Fv/Fm) [Kolber and Falkowski, 1993]

Results Peak Bloom Observations in 2011 (ASP) ASP high ∆ 𝑂 2 /𝐴𝑟 with high T, F negative values with low T, F : lowest value in Dotson Ice Shelf(-7%) higher SST ranging from -1.4˚C to 1.0˚C averaging 0.4 ± 0.4˚C prolonged daylight slightly higher salinity ranging from 33.2 to 34.0 averaging 33.8 ± 0.1 fluorescence large variation 1-14µg/L (5.7 ± 3.2µg/L)

Limited solar radiation Results Peak Bloom Observations in 2011 (SIZ) lower ∆ 𝑂 2 /𝐴𝑟 many less than zero (4.8 ± 8.1%) weaker primary production persistent influence of the waters =accumulated a high respiratory signal cooler SST ranging from -1.8˚C to 0˚C averaging -1.0 ± 0.5˚C Limited solar radiation broad range of salinity lowest salinity : 33.3 lower than ASP thawing sea ice lower fluorescence typically not exceed 4µg/L

Results Declining Bloom Observations in 2012 (ASP) cooler SST reduction in solar radiation shortened daylight periods

Results Declining Bloom Observations in 2012 (ASP) Getz Getz Dotson Dotson PIBP higher SST ahead of the Getz Ice Shelf (DIS) than Dotson Ice Shelf(DIS) both early January and mid-February DIS : warm and saline MCDW entrainment into the surface waters along the western side of the shelf

Results Declining Bloom Observations in 2012 (ASP) decreased ∆ 𝑂 2 /𝐴𝑟 3.8 ± 3.1% wide range -10 to 20% slightly lower salinity 33.6 ± 0.1 fluorescence higher than SIZ 3.7 ± 1.4µg/L

Results Declining Bloom Observations in 2012 (SIZ) decreased ∆ 𝑂 2 /𝐴𝑟 2.2% range 0~8% decreased SST -1.6˚C same average salinity 33.6 similar average 2.8 ± 1.1µg/L

Results Declining Bloom Observations in 2012 (PIBP and SIZ-E) ∆ 𝑂 2 /𝐴𝑟 PIBP : nearly zero (rarely exceed 5%) after phytoplankton bloom period shorter phytoplankton bloom duration and less NPP than the ASP [Arrigo et al., 2012] average SSTs (similar ASP and SIZ) PIBP : -1.4 ± 0.2˚C SIZ-E : -1.5 ± 0.2˚C both average salinity : 33.7 slightly higher than ASP and SIZ both fluorescences < 2µg/L : lower

Results Declining Bloom Observations in 2012

Results Declining Bloom Observations in 2012

Discussion NCPs in the Polynyas NCPs

Discussion NCPs in the Polynyas (spatial variation) 5km by 5km resolution : spatial averaging, 119 ± 68 only positive values ( Polynyas ) the influences of 𝑂 2 deficit and limited gas exchange should be minimal mean flux (both ASP and SIZ) in January 2011 63± 87

Discussion NCPs in the Polynyas (temporal variation) mean NCP in February 2012 = 19% of the NCP from January 2011 PIBP lower than ASP ; observational periods (22~28 Feb 2012) [Arrigo et al., 2012]

Discussion NCPs in the Polynyas satellite-derived primary production (PP) times series (VGPM) f-ratio : new(=export) production to total production January 2011 ~ 0.43 ± 0.07 (n=8) February 2012 ~ 0.34 ± 0.06 (n=21) new production (NP) in steady state systems MODIS Goddard Space Flight Center cumulative PPs during two periods similar average 91 ± 100 Lee et al., [2012] ~ 0.60±0.06 (n=5) NCP during peak : 35~50 [Behrenfeld and Falkowski, 1997] [Dunne et al., 2005] statistically different(t test, p<0.005) [Falkowski et al., 2003]

Discussion Light Availability and/or SST strong positive correlation between and SST : volumetric NCP( ) ~the ratio of NCP to MLD positive correlation between NCP(∆ 𝑂 2 /𝐴𝑟 ) and SST longer surface exposure and higher light availability [Cassar et al., 2011] [Tortell et al., 2012]

3. Accumulated net biological production capacity Discussion Light Availability and/or SST negative correlation between MLD and NCP light availability for high NCPs shallow MLD itself not sufficient ambient water temperature Optimum range for metabolic rate melting [Cassar et al., 2011] [Cassar et al., 2011] 1. Light availability 2. Thermal structure 3. Accumulated net biological production capacity [Tortell et al., 2012]

Discussion Iron (Fe) Limitation 0.21~0.51 Fv/Fm ~ physiological stress on phytoplankton, photo-inhibition, Fe-limitation glacial melt water (~1nM) lower Fv/Fm (< 0.36) in ASP Fe shortage (0.04-0.01nM) occurs during the peak bloom (>10µg/L) higher values in PIBP (near 0.5) enough to sustain bloom [Kolber and Falkowski, 1993; Park et al., 2013]

Summary Significantly higher NCP in the polynyas than sea ice zones Strong temporal variation in NCP between January and February The variation is due to the combined effect of SST, light, and Fe availabilities Early summer ~ light availability, SSTs fueled by Fe Late summer ~ decreased solar radiation, Fe availability

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