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Fritsen, C.H., E. Wirthlin, D. Momberg, E. Murphy and S.F. Ackley. 2010. Bio-optical properties of Antarctic Sea ice during IPY drifting ice stations. Deep Sea Research II doi: 10.1016/j.dsr2.2010.10.028.

Abstract

doi: 10.1016/j.dsr2.2010.10.028

Pack ice in the Bellingshausen Sea contained moderate to high stocks of microalgal biomass (3–10 mg Chl a m-2) spanning the range of general sea ice microalgal microhabitats (e.g. bottom, interior and surface) during the International Polar Year (IPY) Sea Ice Mass Balance in the Antarctic (SIMBA) studies. Measurements of irradiance above and beneath the ice as well as optical properties of the microalgae therein demonstrated that absorption of photosynthetically active radiation (PAR) by particulates (microalgae and detritus) had a substantial influence on attenuation of PAR and irradiance transmission in areas with moderate snow covers (0.2–0.3 m) and more moderate effects in areas with low snow cover. Particulates contributed an estimated 25 to 90% of the attenuation coefficients for the first year sea ice at wavelengths less than 500 nm. Strong ultraviolet radiation (UVR) absorption by particulates was prevalent in the ice habitats where solar radiation was highest— with absorption coefficients by ice algae often being as large as that of the sea ice. Strong UVR-absorption features were associated with an abundance of dinoflagellates and a general lack of diatoms— perhaps suggesting UVR may be influencing the structure of some parts of the sea ice microbial communities in the pack ice during spring. We also evaluated the time-varying changes in the spectra of under-ice irradiances in the austral spring and showed dynamics associated with changes that could be attributed to coupled changes in the ice thickness (mass balance) and microalgal biomass. All results are indicative of radiation-induced changes in the absorption properties of the pack ice and highlight the non-linear, time-varying, bio-physical interactions operating within the Antarctic pack ice ecosystem.

Links:
Deep Sea Research Part II.

C. Fritsen, E. Wirthlin, D. Momberg, J. Memmott, 2010: Seasonal Ultraviolet Radiation and Photosynthetically Active Radiation Absorption Properties of Pack Ice Microbiota in the Southern Ocean. Submitted to: Annals of Glaciology.

Abstract

Comparison of the spectral absorption properties of particulate material in pack ice of the Southern Ocean in winter, spring and summer illustrates a dynamic progression where absorption of photosynthetically active radiation (PAR) is dominated by detritus (and some algae) to a situation where PAR absorption is overwhelmingly dominated by pigmented ice‐biota (a general progression due to the growth and succession of ice microalgal communities). The progression of ultraviolet radiation (UVR) absorption by bulk particulates also follows a similar pattern. However, a more detailed analysis of the UVR‐absorption features of the microalgae show a general lack of UVRabsorbing features in the winter and early spring‐ whereas these features become highly pronounced in the spring and summer. Extremely high UV‐absorption peaks at ~320 nm often become 4‐10 fold higher than absorption peaks attributable to photosynthetic pigments and correspond to absorption peaks of mycosporine‐like amino acids (MAAs). High UVR absorption features occur in microalgae in high light environments in the spring and summer and these features are reduced (or are absent) in ice environments where the UVR and PAR are highly attenuated. Thus, the general progression of enhanced UVR in the spring and summer appears to initiate a seaice, ecosystem‐based response whereby broad expanses of sea ice harbor biota that synthesize MAAs and reduce UVR penetration into the Southern Ocean. The question remains as to whether the enhanced UVR, imparted by the ozone hole, has substantially influenced the structuring of the Antarctic sea ice ecosystems and whether responses in the sea ice have additional implications for physical ice processes or for those processes occurring in the water column.

Links:
Annals of Glaciology

Fritsen, C.H., J.C. Memmott, R.M. Ross, L.B. Quetin, M. Vernet and E.D. Wirthlin. 2010. The timing of sea ice formation and exposure to PAR during austral autumn and winter along the Western Antarctic Peninsula. Polar Biol. DOI 10.1007/s00300-010-0924-7.

Abstract

Understanding the flow of solar energy into ecosystems is fundamental to understanding ecosystem productivity and dynamics. To gain a better understanding of this fundamental process in the Antarctic winter sea ice we produced a model that estimates the time-integrated exposure of seasonal Antarctic sea ice to PAR through the use of remotely sensed sea ice concentrations, sea ice movement and spatially distributed PAR calculations that account for cloud cover and have applied this model over the past three decades. The resulting spatially distributed estimates of sea ice exposure to PAR by mid-winter are evaluated in context of changes in the timing of sea ice formation that have been documented along the Western Antarctic Peninsula (WAP) region and its potential effects on the variation (seasonal and inter-annual) in the accumulation of sea ice algae in this region. The analysis shows the ice pack is likely to have large inter-annual variations (10 to 100 fold) in productivity throughout the autumn to winter transition in the sea ice along the WAP. Moreover, the pack ice is likely to have spatial structure in regards to biological processes that cannot be determined from analysis of sea ice concentration information alone. The resulting inter-annual variations in winter processes are likely to affect the dynamics of Antarctic krill (Euphausia superba).

Links:
Polar Biology

Quetin, L.B., R.M. Ross, C.H. Frtisen and M. Vernet. 2007 Ecological Responses of Antarctic Krill to Environmental Variability: Can We Predict the Future? Antarctic Science, 253-266.

Abstract

The first winter in the life cycle of Antarctic krill is a critical period in which larval survival and recruitment to the adult population are highly sensitive to environmental conditions, yet little is known about larval physiological dynamics during this period. An individual-based model was developed to investigate patterns of larval krill growth and condition factor in response to environmental variability during fall and winter, west of the Antarctic Peninsula. Field and experimental observations from Southern Ocean Global Ocean Ecosystems Dynamics cruises in 2001 and 2002 and the Palmer Long-Term Ecological Research program were used to parameterize the model. Growth was modeled by partitioning total body carbon between length and condition factor. Total body carbon was simulated with empirical temperature-dependent rates of ingestion of phytoplankton and respiration, and ingestion of algae grown on a surface to simulate sea ice algae. Light-driven diel vertical migration modulated ingestion of phytoplankton and sea ice algae as a function of latitude, season and sea ice cover. Simulations highlighted three environmental processes controlling food availability, and consequently, physiological condition of krill: the fall phytoplankton decline, sea ice advance and development of sea ice microbial communities, and the late winter increase in sea ice microbial community biomass. Fall phytoplankton dynamics were identified as a major driver of larval krill physiological condition throughout this critical period. The model presents a mechanism linking larval krill survival and recruitment to fall and winter variability in phytoplankton and sea ice dynamics along the western Antarctic Peninsula.

Lowe, A.T., R.M.Ross, L.B. Quetin, M.Vernet, and C.H. Fritsen, 2012. Simulating larval Antarctic krill growth and condition factor during fall and winter in response to environmental variability. Mar Ecol Prog Ser. Vol 452: 27-43 doi: 10.3354/meps09409.

Abstract

The first winter in the life cycle of Antarctic krill Euphausia superbais a critical period in which larval survival and recruitment to the adult population are highly sensitive to environmental conditions, yet little is known about larval physiological dynamics during this period. An individual-based model was developed to investigate patterns of larval krill growth and condition factor in response to environmental variability during fall and winter, west of the Antarctic Peninsula. Field and experimental observations from Southern Ocean Global Ocean Ecosystems Dynamics cruises in 2001 and 2002 and the Palmer Long-Term Ecological Research program were used to parameterize the model. Growth was modeled by partitioning total bodycarbon between length and condition factor. Total body carbon was simulated with empirical temperature-dependent rates of ingestion of phytoplankton and respiration, and ingestion of algae grown on a surface to simulate sea ice algae. Light-driven diel vertical migration modulated ingestion of phytoplankton and sea ice algae as a function of latitude, season and sea ice cover. Simulations highlighted 3 environmental processes that controlled food availability, and consequently, physiological condition of krill: the fall phytoplankton decline, sea ice advance and development of sea ice microbial communities, and the late winter increase in sea ice microbial community biomass. Fall phytoplankton dynamics were identified as a major driver of the physiological condition of larval krill throughout this critical period. The model presents a mechanism that links larval krill survival and recruitment to fall and winter variability in phytoplankton and sea ice dynamics along the western Antarctic Peninsula.

Vernet, M., W.A Kozlowski, L. Yarmay, A.T. Lowe, R.M. Ross, L.B. Quetin, and C.H. Fritsen, 2012. Dynamics of phytoplankton bloom demise during the austral fall in the western Antarctic Peninsula. Mar Ecol Prog Ser.452:45-61 doi-10.3354/meps09704.

Abstract

Antarctic phytoplankton is characterized by a pronounced seasonality in abundance, driven mainly by changes in sunlight. We combined measurements and modeling to describe the influence of changing daylength on fall and winter phytoplankton production in coastal waters of the western Antarctic Peninsula (wAP) in 2001 and 2002. The model was parameterized with field observations from the Palmer Long-Term Ecological program in the wAP during summer and early fall and from the Southern Ocean Global Ecosystems Dynamics program fall and winter cruises to Marguerite Bay and shelf waters. Shorter daylength and a deepening of the mixed layer account for most of the decrease in primary production during March, April, and May. At this time, biomass decreases by an order of magnitude and remains low and constant until the end of August. An additional loss rate was added to the primary production model to fit output to observations. This loss rate, estimated at ~0.1 to 0.15 d−1, is due to physical, chemical, and biological processes such as scavenging by sea ice, zooplankton grazing, cell lysis, and cell sedimentation, which are expected to be high at this time of year. Growth and loss rates of phytoplankton populations are similar on 1 March, with growth decreasing rapidly over time while the loss rates remain constant. By the beginning of winter (1 June), growth is low, with minimum rates in July and increasing towards September. During a period of diminishing food supply, preliminary estimates of grazing indicate that fall biomass could support existing macrozooplankton populations, but the timing and concentration of food supply is variable and expected to affect health of zooplankton as they enter the winter.