1. A decadal analysis of phytoplankton community composition in the melting West Antarctic Peninsula
Oscar Schofield1 Grace Saba1, Zoe Finkel2, Andrew Irwin2, Vincent Saba3, Hugh Ducklow4
1Rutgers University, Mount Allison University, NOAA, 3National Marine Fisheries Service, 4Lamont Doherty Earth Observatory & Columbia University
The West Antarctic Peninsula (WAP) is melting
l mid-winter surface atmospheric temperatures are increasing at >5x the global average over the last 50 years1,2
l 87% of the glaciers are in retreat, sea ice season has shortened by 90 days, and perennial sea ice is no longer a feature of northern WAP3,4,5
l There have been large observed declines in northern WAP summer phytoplankton biomass which affects the food web that is tightly coupled to the primary producers6,7
Using CHEMTAX, the dominant phytoplankton taxon present in the LTER coastal time series were diatoms. Cryptophytes were second most dominant phytoplankton taxon present.
Diatoms and cryptophyte are segregated in T/S space. Cryptophytes associated with colder & fresher meltwater.
(size of circle indicates in situ chlorophyll a concentration) 32 33 34
Salinity -1 1 2 3 -2
Temperature
B) cryptophytes
D) prasinophytes
A) diatoms
C) mixed flagellates
100 50
% chlorophyll a associated with phytoplankton taxa
01/01/95
01/01/05
Date (day/month/year)
E) type-4 haptophytes
Diatoms
Cryptophytes
Given the scale of the change, we are interested in assessing if it being accompanied by major shifts in the phytoplankton community composition. To address this we are tracking the major phytoplankton taxa over time using HPLC-derived taxonomic pigments.
100
Palmer LTER Site: The Palmer LTER has collected a 22-year time series along the West Antarctic Peninsula. Each year from October through March, the team biweekly samples the coastal waters, via zodiac (weather permitting). The data in this analysis is drawn from the bulk of data collected at Stations B & E (red stars). This poster focuses on the more oceanic station E.
Litchfield Island
Arthur Harbor
Bonaparte Point
Janus
Island
Hermit Island
Palmer
Station
Anvers Island
Torgersen Island
’ W ’S ‘S A C D E B
A recent analysis by Saba et al. (2014)7 showed the magnitude of the summer phytoplankton blooms is correlated with the preceding winter/spring ice concentrations, where increased water column stability was associated with increased winter ice extent/duration and reduced spring/summer winds. Based on this analysis:
l The largest blooms are associated with diatoms.
l When the chlorophyll a concentration drops the relative proportion of cryptophytes increases.
l Stepwise regression analysis shows increased stratification (associated with melt-water and low wind) is significantly (p<<0.05) associated with cryptophytes while the conditions promoting deeper mixing are associated with diatoms.
The other significant taxa were mixed flagellates, prasinophytes & type-4 haptophytes that were present in background populations with lower interannual variability. Mixed flagellates did have 2 years with significant blooms out of the 14 years analyzed. The dotted red line indicates the 50% line for the chlorophyll a. 50
Diatoms and cryptophyte blooms do not co-occur
(size of black circle indicates in situ chlorophyll a concentration)
Fucoxanthin (ng mL-1)
Percent of chlorophyll a
associated with diatoms
associated with cryptophytes
200
400
600
800 40
140
180
Alloxanthin
(ng mL-1)
Diatom Marker Pigment
Marker Pigment
Cryptophyte
Predictions for the future WAP: Global climate model projections suggest a continued increase in the strength of warm, north-westerly winds8 and decline in sea ice9, which will reduce water column stability. This will decrease overall productivity. Increased warming will also be associated with enhanced glacial melt. While decreased water column stability favors diatoms, the increase in melt water will favor crypotphytes. Resolving “who wins” is a critical question as the potential shift to small cryptophyte cells (<10 microns) from larger diatoms (>10 microns) is of key biogeochemical and ecological significance. Small phytoplankton cells has been associated with decreased clearance rates of the Antarctic krill10 (the keystone species for the WAP food web) and with decreased rates of atmospheric CO2 sequesteration11. Food web modeling suggests the transition to small cells is already occurring12.
Summer chlorophyll a shows a great deal of interannual variability (data below is from Station E). There is no discernable long term trend in the seasonal chlorophyll a over the course of the LTER time series.
The largest seasonal blooms are associated with diatoms
Monthly Log transformed chlorophyll a
% of chlorophyll a
with diatoms or
cryptophytes
Acknowledgements: The Palmer LTER data set reflects the team effort of countless scientists and contractors. However special thanks and recognition is reserved for Barbara Prezelin and Maria Vernet who collected a“gold” standard of phytoplankton data. The support of the National Science Foundation (ANT ) and the LTER network is also acknowledged.
References: 1: Skvarca et al. 1999, 2: Vaughan et al Cli. Change, 3: Cook et al Science, 4: Martinson et al Deep Sea Res., 5: Stammerjohn et al. Deep Sea Res., : Montes Hugo et al Science, 7: Saba et al Nature Comm. (in revision), 8: Hall & Visbeck 2002 J. Clim., 9: Liu et al , 10: McClatchie & Boyd 1983 Can. J Fish. & Aquat. Sci., 11: Montes Hugo In prep, 12: Sailey et al MEPS.