Antarctica, Climate Change, and Krill: Dr. Grace Saba
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Antarctica, Climate Change, and Krill: Dr. Grace Saba

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Dr. Grace Saba, Rutgers University, presented on her work in Antarctica with Antarctic krill and ocean acidification at the October 23, 2013 STEM Educators' Series.

Dr. Grace Saba, Rutgers University, presented on her work in Antarctica with Antarctic krill and ocean acidification at the October 23, 2013 STEM Educators' Series.

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  • Thank you for this opportunity, I am excited and happy to be here today to talk about my work, which currently focuses on Antarctic food webs, climate change, specifically ocean acidification, and Antarctic krill.
  • The Earth has a natural greenhouse effect which in this simple picture is in a sort of equilibrium. Carbon dioxide, or CO2, is taken up by plants in the process of photosynthesis, CO2 is respired by other organisms, and the ocean exchanges CO2 with the atmosphere. CO2 is considered a greenhouse gas, in that it absorbs heat. This heat is trapped in the Earth’s atmosphere. The earth's "greenhouse effect" is what makes this planet suitable for life as we know it. The oceans play a major role in the Global Carbon cycle and this natural greenhouse effect because of the exchange of CO2 with the atmosphere.
  • Since the end of the first Industrial Revolution in the 1830s, widespread burning of fossil fuels, deforestation, and cement production have released more than 440 billion metric tons of CO2 into the atmosphere (half of that in the last 30 years). This mass release of previously “locked away” carbon enhances the natural greenhouse effect, trapping more and more heat in our atmosphere. That’s one problem with CO2.Notes: Cement manufacturing releases CO2 in the atmosphere both directly when calcium carbonate is heated, producing lime and carbon dioxide, and also indirectly through the use of energy of its production involves the emission of CO2
  • This rise in atmospheric greenhouse gas concentrations has greatly increased the global average temperatures. This figure shows AN AVERAGE OF MODELED PREDICTIONS of global mean temperature resulting from ‘business as usual’ emissions in greenhouse gases following on from observed changes since 1860 (orange curves). The addition of sulphate aerosol cooling is shown in the red curves.NOTES: Doubling of CO2 is equivalent to a temperature increase of about 1.5 degrees C on a timescale of 50-100 years (Geoffrey Vallis, GFDL).Sulfates aerosols are salts in the atmosphere that contain a charged group of sulfur and oxygen atoms: SO42-, the basic constituent of sulfuric acid. Aerosols can cool the climate in two basic ways: either directly, under clear sky conditions, by reflecting away some of the incoming solar radiation, or indirectly, by increasing the reflectivity of clouds. However the United Nations Framework Convention on Climate Change has noted that sulfate aerosols remain in the atmosphere for only a short amount of time in comparison to other greenhouse gases, and therefore their cooling is localized and temporary. Other side effects of sulfate aerosols in the environment include poor air quality.
  • Now keep in mind that oceans absorb atmospheric heat, so an increase in temperature will increase the amount of heat, termed heat content, in the upper 700 m of the global ocean.
  • I am going to focus my presentation today specifically on how Antarctica is being impacted by climate change.Antarctica is the southernmost continent. Contrary to the US, Antarctica is in the Southern Hemisphere, which means summer in the US is the winter in Antarctica. Most scientists conducting research in Antarctica do so in the austral summer (Nov-Mar), where temperatures average about freezing, or 0 degrees C.Antarctica, on average, is the coldest, driest, and windiest continent, and has the highest average elevation of all the continents.Antarctica is considered a desert, because the continent receives very little precipitation. The temperature in Antarctica has reached −89 °C. There are no permanent human residents, but anywhere from 1,000 to 5,000 people reside throughout the year at the research stations scattered across the continent. Only cold-adapted organisms survive there, and many of the marine animals contain an anti-freeze protein so they do not freeze.
  • The Antarctic continent is surrounded by a circumpolar current, called the Antarctic Circumpolar Current, or ACC. The ACC is the world’s largest ocean current, and this current is fed by warmer waters from the north. Thus the ACC is Antarctica’s warmest water. Its temperature ranges between 0 and 5 degrees, but for Antarctica, this is considered warm water. The West Antarctic Peninsula, or WAP, is the location where the ACC is closest to the continent.The location of the ACC in proximity to the WAP is also the reason this location is warming much more quickly than other parts of Antarctica, which I will show you next.
  • The West Antarctic Peninsula, or WAP, has undergone profound warming in the past decades; thus it is an appropriate location to study how rapid warming can alter food webs.Mid-winter surface atmospheric temperatures have increased by 6°C (>5x the global average) in the past 50 years. This is shown in the left figure with the waters near the WAP in red showing a +0.2 degrees C per year increase over the last 50 years.Warming air temperatures are also associated with the increase in the heat content of seawater near the WAP, shown as an increasing trend since 1992 in the figure on the right.Additionally, sea ice is declining. 87% of the WAP glaciers are in retreat, the ice season has shortened by nearly 90 days, and perennial sea ice (sea ice older than one year; thicker ice, ranges 6.5-16.5 ft thick) is no longer a feature of this environment. These changes are accelerating.
  • The rapid increase in global temperatures is causing the ocean and the continent to change drastically in our lifetime. This is an image of Palmer Station, Antarctica in 1990.
  • This is Palmer Station 20 years later. Glacial rock is now exposed throughout the year.
  • And this exposure has allowed the growth of green land plants at Palmer station. And since the past few years, there is even a species of mushroom growing.
  • These rapid changes are associated with recent changes in WAP phytoplankton.With increased warming over the past 30 years, the magnitude of chl a in the entire WAP region has decreased by 12%. Chl a is the major photosynthesizing pigment in phytoplankton, thus it is used as a proxy for phytoplankton biomass. The changes have been particularly dramatic in the northern WAP region, depicted here in blue which shows negative changes in chlorophyll from more recent years(1998-2006) compared to the 1970s-80s. These declines are driven by an increase in cloudy days, deep mixed layers associated with persistently strong winds, and a reduction in the marginal ice zone.Not only is phytoplankton biomass declining, but the phytoplanktoncommunity composition in this region, especially the northern region, has shifted from large to small cells. This is depicted in this figure on the right which compares the contribution of phytoplankton communities dominated by large (20um) versus small (20um) cells to total chlorophyll concentration in past (1970s-1980s) and recent (1998-2006). This shift in cell size has been attributed to shifts from large diatoms to small flagellates called cryptophytes. This shift is associated with warmer temperatures and lower salinity waters caused from glacial meltwater in this region.NOTES:Nbin/Nmode is the relative frequency of observations per bin, normalized by the modeIn the southern WAP, ice retreat has allowed localized increases in diatom-driven primary productivity.
  • We believe the changes in phytoplankton, which are the base of the food web, are creating changes in their predators, the zooplankton including Antarctic krill. Krill can not efficiently feed on smaller sized phytoplankton cells, and as small cells have increased in the recent decades, krill have declined nearly two-fold in this region since the mid-1970s.
  • And even farther up the food chain, we are seeing drastic declines in Adelie penguins in the WAP region (% remaining over time shown in red line). The Adelie penguin population seems to be becoming replaced by suppolar penguin species, the Gentoos and Chinstraps, shown by green and blue lines respectively.
  • Adelie penguins, in the past, received half of their nutrition from silverfish. Silverfish are now absent in the northern region of the WAP because of the rapid warming and decline in ice. Now Adelie penguins are dependent almost solely on krill in the northern region, and so with the krill decline, so have the Adelie penguins.Gentoos and chinstrap penguins, however, can dive deeper than Adelie penguins and thus can feed on deep water fish called myctophids. Thus they are able to utilize food other than krill and so are increasing in the northern region.As warming continues, we believe the warming conditions in the northern regions will migrate south, thus endangering krill and Adelie penguins along the entire peninsula.Any questions so far?
  • I have mainly discussing the temperature problem from rising CO2, but….In addition to increasing temperature due to increasing CO2, the other CO2 issue is this: Nearly 1/3 of anthropogenic CO2 emissions is absorbed by the oceans, at a rate of 1 million metric tons of CO2 per hour. The shift in the ocean towards more acidic conditions is happening because of this ever-increasing amount of CO2 in the atmosphere. This is known as ocean acidification. It occurs when CO2 reacts with sea water to produce an acid. The faster the increase of CO2 in the atmosphere, the faster the acidification of the ocean. Ocean acidification is a topic which is gaining attention, both in scientific research and the public eye.
  • This is an updated figure of the Keeling curve showing the increase in CO2 (red line) at the Hawaiian Ocean Time series at Mauna Loa over the past 50 years. This is shown in ppmv or parts per million volume, which is the volume of CO2 per million volumes of air.Anthropogenic emissions have driven the rapid 40% increase in atmospheric carbon dioxide (CO2), from preindustrial levels of 280 ppm to current levels of nearly 400 ppm. Sampling for atmospheric CO2 started at the Mauna Loa Hawaii observatory in 1960, and monthly seawater sampling at Station Aloha has occurred since 1990. As CO2 has increased in the atmosphere, pCO2, or the partial pressure or amount of CO2 in seawater, (blue line; measured monthly since 1990 at Station Aloha) has increased and the pH of the surface seawater at Station Aloha (green line) has dropped by about 0.1 pH unit. That is equivalent toa 28% increase in ocean acidity. Current CO2concentrations are projected to double by the end of the 21st century. The Intergovernmental Panel on Climate Change (IPCC) predicts an additional drop of 0.2 to 0.3 pH units by the end of this century. That is a 100-150% increase in ocean acidity since before the industrial revolution.
  • Today there is a rich, diverse, and mostly endemic marine fauna associated with Antarctica. Many benthic calcifying fauna are prominent in nearshore communities and are economically and/or ecologically important (e.g., bivalves, such as mussels and oysters, sea urchins, limpets, brachiopods, cold water corals).A striking difference between the benthic communities of north and south polar regions is the near absence of shell-crushing predators in the Antarctic, which are common in the Arctic such as clawed crabs, lobsters and heavily jawed fish. This is due to the extremely low seawater temperatures (-2C) that occur in nearshore Antarctica. As a result, Antarctic benthic invertebrates evolved to have thin, weakly calcified shells.
  • Here I am showing data from a study by Jim McClintock and colleagues showing dissolution (depicted by increasingly negative mean adjusted difference in shell mass on the x-axis here) of multiple benthic invertebrates (bivalve, limpet, and brachiopod) exposed to pH levels of 7.4 compared to control ambient pH levels of 8.2. Within a period of only 14–35 days, shells of all four species held in pH 7.4 seawater had suffered significant dissolution.The bottom figure shows micrographs of the shell surface of the bivalve Yoldiaeightsi exposed for 56 days to control pH (8.2) and acidified seawater with pH of 7.4. Calcium carbonate prisms indicating dissolution are visible in the acidified shell.
  • As I mentioned before, up to the present, there was a lack of shell crushing predators in the Antarctic due to the extremely low seawater temperatures (-2C) that occur in nearshore Antarctica. As a result, Antarctic benthic invertebrates evolved to have thin, weakly calcified shells.However, recent warming sea temperatures due to rising CO2 levels are allowing shell-crushing, deep water king crabs to invade the continental shelves surrounding Antarctica, some of which are being collected for study in this photo; thus any additional weakening of invertebrate shells owing to ocean acidification will render them even more vulnerable to these predators.The coupling of rising temperatures, ocean acidification, and predator invasion is expected to influence both planktonic and benthic marine communities of Antarctica.
  • This figure shows representative examples of impacts of ocean acidification on major groups of marine biota derived from experimental manipulation studies. The response curves on the right indicate four cases: (a) linear negative, (b) linear positive, (c) level, and (d) nonlinear parabolic responses to increasing levels of seawater pCO2 for each of the groups. The first thing to note is that in some cases strains of the same species exhibited different behavior in different experiments, so we still do not fully understand the physiological mechanisms behind these non-uniform responses. The second thing to note is the limited number of studies on non-calcifying organisms. Most ocean acidification studies up to date have focused on biocalcification rates in corals, shellfish, and planktonic organisms. However, other processes may also be directly or indirectly affected by an increase in CO2 including primary productivity, plankton community composition, food web dynamics, metabolism of secondary/tertiary producers, and biogeochemistry including carbon and nitrogen cycling. Increases in atmospheric CO2 and subsequent ocean sequestration are paralleled with alterations in oceanic carbonate chemistry, which may affect biogenic calcification, photosynthesis, community composition, and biogeochemistry of planktonic organisms. As the ocean becomes more acidic, it makes it harder for marine animals that build their shells out of calcium carbonate, like corals, molluscs such as oysters, sea urchins, and calcifying planktonic organisms such as coccolithophores and foraminifera. As you can imagine, this can have a direct impact on the seafood that we eat and negatively affect the world’s economy.Research has already found that corals,[32][33][34]coccolithophore algae,[35][36][37][38] coralline algae,[39] foraminifera,[40]shellfish[41] and pteropods[10][42] experience reduced calcification or enhanced dissolution when exposed to elevated CO2. The Royal Society of London published a comprehensive overview of ocean acidification, and its potential consequences, in June 2005.[15] However, some studies have found different response to ocean acidification, with coccolithophore calcification and photosynthesis both increasing under elevated atmospheric pCO2,[43][44][45] an equal decline in primary production and calcification in response to elevated CO2[46] or the direction of the response varying between species.[47] Recent work examining a sediment core from the North Atlantic found that while the species composition of coccolithophorids has remained unchanged for the industrial period 1780 to 2004, the calcification of coccoliths has increased by up to 40% during the same time.[45] While the full ecological consequences of these changes in calcification are still uncertain, it appears likely that many calcifying species will be adversely affected. When exposed in experiments to pH reduced by 0.2 to 0.4, larvae of a temperate brittlestar, a relative of the common sea star, fewer than 0.1 percent survived more than eight days.[26] There is also a suggestion that a decline in the coccolithophores may have secondary effects on climate, contributing to global warming by decreasing the Earth's albedo via their effects on oceanic cloud cover.[48]Aside from calcification, organisms may suffer other adverse effects, either directly as reproductive or physiological effects (e.g. CO2-induced acidification of body fluids, known as hypercapnia), or indirectly through negative impacts on food resources.[15] Ocean acidification may also force some organisms to reallocate resources away from productive endpoints such as growth in order to maintain calcification.[49] It has even been suggested that ocean acidification will alter the acoustic properties of seawater, allowing sound to propagate further, increasing ocean noise and impacting animals that use sound for echolocation or communication.[50] However, as with calcification, as yet there is not a full understanding of these processes in marine organisms or ecosystems.[51]Leaving aside direct biological effects, it is expected that ocean acidification in the future will lead to a significant decrease in the burial of carbonate sediments for several centuries, and even the dissolution of existing carbonate sediments.[52] This will cause an elevation of ocean alkalinity, leading to the enhancement of the ocean as a reservoir for CO2 with moderate (and potentially beneficial) implications for climate change as more CO2 leaves the atmosphere for the ocean.[53]While much emphasis has been placed on rates of biocalcification, the effects of CO2 on plankton community composition, food web dynamics, and carbon and nitrogen cycling remain unanswered.
  • Diatoms are associated with large blooms in the Southern Ocean, and are the base of the classical food chain in all regions globally which allows rapid trophic transfer of C to higher organisms such as krill, fish, penguins, and whales.There have been a few ocean acidification mesocosm studies completed in the Ross Sea, Antarctica, which is south of the WAP. In a study conducted by Tortell and colleagues, enhanced pCO2 increased the relative growth rate and primary productivity of the assemblage. They also saw a transition to a small celled prymesiophyte called Phaeocystis in the lower CO2 treatments and a transition to diatoms in the higher CO2 treatment. Again, ppmv is parts per million volume, which is the volume of CO2 per million volumes of air. There were also shifts within the diatom community: from a small pennate diatom to the large chain-forming diatom Chaetoceros in the highest CO2 treatment. The important thing to take away from this is that, ocean acidification does not always impact organisms negatively. Diatoms responded favorably to higher CO2 concentrations likely because it decreased their energetic requirement to concentrate CO2 for photosynthesis and growth.
  • This scenario shows diatoms experiencing positive growth and productivity under higher CO2/more acidic conditions. Large diatoms will favor transfer of C to higher trophic levels such as krill, penguins, and whales. However, higher biomass and productivity of large diatoms will also increase nutrient utilization and may drive the system to nutrient-limitation over longer timescales, and this needs to be considered in future manipulations.
  • This slide shows preliminary results from a perturbation experiment I conducted in the northern WAP at Palmer Station. In contrast to the large diatom-dominated system: we did see a CO2 response in this small-phytoplankton dominated system.Both biomass and primary productivity were lower in the high CO2 treatment compared to the 2 lower CO2 treatments, and biomass and productivity did not increase over time compared to the lower CO2 treatments. P value is a common statistical term used to help determine the significance of your results; a p-value of less than 0.05 means that you are 95% confident that the results are statistically and significantly different, in this case the prim prod and abundance of nanophytoplankton are statistically significantly lower in the high CO2 treatment compared to the ambient and low CO2 treatments.
  • One of the big questions in ocean acidification research is: do different growth phases of organisms respond differently to ocean acidification?A majority of ocean acidification studies observing growth and development in zooplankton show decreased hatching success, irregular larval development, or decrease in larval size under conditions of high CO2 or low pH.This is a picture from a study conducted by So Kawaguchi and colleagues determining the effects of enhanced seawater CO2 on Antarctic krill embryos. They found that embryos had irregular development or did not develop at all under marine conditions of 2000 ppm pCO2 (right panel) compared to normal development in embryos exposed to ambient CO2 levels (left panel). And again, pCO2 is the partial pressure or amount of CO2 in seawaterThese results have implications for long-term population dynamics of Antarctic krill.
  • Aquatic organisms (water breathers) rely almost entirely on ion exchange mechanisms to maintain acid-base balance. This is a very simple diagram of ions (such as hydrogen ions, sodium, etc) being transported from outside of the membrane to the inside.
  • I know this figure looks scary, and I won’t go into the exact physiological details for everything, but I wanted to just touch on a few main points. Under high CO2/decreased pH, there is an influx of H+ ions through the membrane and bicarbonate ions accumulate. Ion regulation will strive to re-establish original or new equilibria in the body fluids. This effort to equilibrate, or compensate, for these changes causes large and perhaps unfavorable changes in the ionic composition of plasma and other body fluids. This can cause a decrease in protein synthesis rate, a decrease in heart and muscle function, and increases or decreases in ventilation, or breathing rate.Organisms that show a drop in breathing rate typically just shut down all of their metabolic processes, called metabolic suppression.Organisms that show an increase in ventilation rate typically increase their overall metabolism because they compensate to get back to original acid-base balance.These organisms have higher demands for acid-base regulator proteins and would have to work harder to maintain or alter internal acid-base equilibria. Furthermore, their oxygen transport system may be compromised, making them less effective at picking up oxygen (O2) and forcing them to process more water to extract the O2 they demand. THERE IS LIKELY AN ENERGETIC AND PHYSIOLOGICAL COST TO THIS COMPENSATION.Both responses have the potential to negatively affect growth and reproduction.
  • Increased growth and metabolism was also observed in brittle stars at reduced pH/elevated CO2
  • but the cost - muscle wastage - was substantial.Longitudinal cross sections of established brittle star arms mounted in methacrylate resin and stained with Lee’s basic blue fuchin.
  • Euphausiasuperba responded to elevated CO2 by increasing ingestion rates, nutrient release rates, and metabolic activity, reflecting enhanced energetic requirements of acid-base regulation, but the associated compensation costs included the catabolism of proteins and differential partitioning of C and N, which created stoichiometric changes within the krill which could, in the long-term, decrease growth and reproduction and negatively impact an already declining krill population.
  • Euphausiasuperba responded to elevated CO2 by increasing ingestion rates, nutrient release rates, and metabolic activity, reflecting enhanced energetic requirements of acid-base regulation, but the associated compensation costs included the catabolism of proteins and differential partitioning of C and N, which created stoichiometric changes within the krill which could, in the long-term, decrease growth and reproduction and negatively impact an already declining krill population.
  • Euphausiasuperba responded to elevated CO2 by increasing ingestion rates, nutrient release rates, and metabolic activity, reflecting enhanced energetic requirements of acid-base regulation, but the associated compensation costs included the catabolism of proteins and differential partitioning of C and N, which created stoichiometric changes within the krill which could, in the long-term, decrease growth and reproduction and negatively impact an already declining krill population.
  • So Antarctic pteropods with generation times of 0.6-1.5 years will only have 11-27 to adapt to corrosive seawater predicted by the year 2030.EXTRA:If unabated CO2 emissionscontinue and surface waters of the Southern Ocean and portionsof the Subarctic Pacific become undersaturated with respect to aragoniteby 2100 as projected (Orr et al., 2005), then shelled pteropodsin these regions would have only 50–150 generations toadapt to corrosive seawater, given that high-latitude pteropodsare thought to have generation times of 0.6–1.5 years(Kobayashi, 1974; Bathmann et al., 1991; Dadon and de Cidre,1992; Gannefors et al., 2005). Generation times for spinosespecies of foraminifera are frequently linked with the lunar cyclesuch that they reproduce every 2–4 weeks; however, non-spinosespecies probably have longer reproductive cycles (Hemleben et al.,1989). Shorter generation time affords increased opportunities formicroevolutionary adaptation.
  • So Antarctic pteropods with generation times of 0.6-1.5 years will only have 11-27 to adapt to corrosive seawater predicted by the year 2030.EXTRA:If unabated CO2 emissionscontinue and surface waters of the Southern Ocean and portionsof the Subarctic Pacific become undersaturated with respect to aragoniteby 2100 as projected (Orr et al., 2005), then shelled pteropodsin these regions would have only 50–150 generations toadapt to corrosive seawater, given that high-latitude pteropodsare thought to have generation times of 0.6–1.5 years(Kobayashi, 1974; Bathmann et al., 1991; Dadon and de Cidre,1992; Gannefors et al., 2005). Generation times for spinosespecies of foraminifera are frequently linked with the lunar cyclesuch that they reproduce every 2–4 weeks; however, non-spinosespecies probably have longer reproductive cycles (Hemleben et al.,1989). Shorter generation time affords increased opportunities formicroevolutionary adaptation.
  • So Antarctic pteropods with generation times of 0.6-1.5 years will only have 11-27 to adapt to corrosive seawater predicted by the year 2030.EXTRA:If unabated CO2 emissionscontinue and surface waters of the Southern Ocean and portionsof the Subarctic Pacific become undersaturated with respect to aragoniteby 2100 as projected (Orr et al., 2005), then shelled pteropodsin these regions would have only 50–150 generations toadapt to corrosive seawater, given that high-latitude pteropodsare thought to have generation times of 0.6–1.5 years(Kobayashi, 1974; Bathmann et al., 1991; Dadon and de Cidre,1992; Gannefors et al., 2005). Generation times for spinosespecies of foraminifera are frequently linked with the lunar cyclesuch that they reproduce every 2–4 weeks; however, non-spinosespecies probably have longer reproductive cycles (Hemleben et al.,1989). Shorter generation time affords increased opportunities formicroevolutionary adaptation.
  • So Antarctic pteropods with generation times of 0.6-1.5 years will only have 11-27 generations to adapt to corrosive seawater predicted by the year 2030.Antarctic krill with a lifespan of 5-7 years will only have 2.5-3.5 generations to adapt to corrosive seawater predicted for the Southern Ocean by the year 2030.EXTRA:If unabated CO2 emissionscontinue and surface waters of the Southern Ocean and portionsof the Subarctic Pacific become undersaturated with respect to aragoniteby 2100 as projected (Orr et al., 2005), then shelled pteropodsin these regions would have only 50–150 generations toadapt to corrosive seawater, given that high-latitude pteropodsare thought to have generation times of 0.6–1.5 years(Kobayashi, 1974; Bathmann et al., 1991; Dadon and de Cidre,1992; Gannefors et al., 2005). Generation times for spinosespecies of foraminifera are frequently linked with the lunar cyclesuch that they reproduce every 2–4 weeks; however, non-spinosespecies probably have longer reproductive cycles (Hemleben et al.,1989). Shorter generation time affords increased opportunities formicroevolutionary adaptation.
  • Purple = business as usual (no reductions on emissions)Bright green B1 = greatly reduced emissionsPPMV- define
  • Marine snails called pteropods can reach densities of 1000s to 10,000 individuals m-3 in high-latitude areas and comprise up to 25% of total zooplankton biomass in the Southern Ocean. They are an important prey species for a variety of other zooplankton and fish, and they contain a soluble calcium carbonate shell.Brad, the co-investigator on the project has worked with these organisms in the recent past.
  • There has been much recent focus on these organisms. In this study by Orr and colleagues, significant dissolution of the shell of the pteropod Clio pyramidata occurred within only 48 hours when exposed to undersaturated seawater. These results suggest that in only 18 years from now, we will likely see major changes in the presence of this organism in Antarctic waters.
  • Circumpolar risk maps of krill hatching success under projected future pCO2 levels. a–d,Hatching success under the RCP 8.5 emission scenariofor 2100 (a) and 2300 (b); and under the RCP 6.0 emission scenario for 2100 (c) and 2300 (d). Note the different colour scales on each panel. Thesouthern-most black line shows the northern branch of the Southern Antarctic Circumpolar Current Front, and the northern-most line shows the middlebranch of the Polar Front.We generated risk maps for the hatching success in a futureacidified Southern Ocean based on pCO2 projections of the waterlayers that krill embryos sink through during the first 3 days. TheWeddell Sea and the Haakon VII Sea are identified as the firstareas where krill egg hatching success is most likely to be at risk(Fig. 4). The predicted risk for the RCP 6.0 scenario (mediumhighemission) is much milder compared with that for the RCP 8.5scenario (high emission without mitigation), but still with hatchingsuccess by the year 2300 being as low as 45% of the present level.Under the RCP 8.5 scenario most of krill habitat willsuffer at least 20% lower hatching success by 2100, with reductionsof up to 6070% in the Weddell Sea. The entire habitat maybe unsuitable for hatching by the year 2300 (Fig. 4b) and thiswould lead to the collapse of the krill population.
  • This figure shows observed and projected changes in the global average temperature under 3 IPCC no-policy emissions scenarios. The shaded areas show the likely ranges while the lines show the central projections from a set of climate models. A wider range of model types shows the outcomes from 2-11.5 degrees F. Changes are relative to the 1960-1979 average.For the next two decades, a warming of about 0.2°C per decade is projected for a range of SRES emission scenarios. Even if the concentrations of all greenhouse gases and aerosols had been kept constant at year 2000 levels, a further warming of about 0.1°C per decade would be expected.
  • Anthropogenic warming and sea level rise would continue for centuries due to the time scales associated with climate processes and feedbacks, even if greenhouse gas concentrations were to be stabilized
  • National Center for Atmospheric Research Community Climate System Model 3.1 (CCSM3) modelled decadal mean pH at the sea surface for 1875, 1995, 2050 and 2095. Source after Feely et al., Oceanography (2009).
  • These rapid changes are associated with recent changes in WAP phytoplankton.With increased warming over the past 30 years, the magnitude of chl a has decreased by 12%. The changes have been particularly dramatic in the northern WAP, with declines driven by an increase in cloudy days, deep mixed layers associated with persistently strong winds, and a reduction in the marginal ice zone.Dominant algal groups in region are diatoms andcryptophytes, butprymnesiophytes can sometimes contribute to the overall population. The algal community composition in this region, especially the northern region, has shifted from large to small cells, in particular flagellates from the genus Cryptomonas.This shift is associated with warmer temperatures and lower salinity waters caused from glacial meltwater in this region, as shown by this figure.In the southern WAP, ice retreat has allowed localized increases in diatom-driven primary productivity.

Antarctica, Climate Change, and Krill: Dr. Grace Saba Antarctica, Climate Change, and Krill: Dr. Grace Saba Presentation Transcript

  • Antarctica, Climate Change, and Krill Grace K. Saba Rutgers University saba@marine.rutgers.edu
  • Humans are Impacting the Ocean
  • Rising Temperature: The CO2 Problem 18 17 •Increased atmospheric temperature Temperature (° C) Increase in CO2 causes: 16 15 14 13 1860 1880 1900 1920 1940 1960 1980 2000 2020 2040 2060 2080 2100 Y ear Hadley Centre for Climate Prediction and Research
  • Rising Temperature: The CO2 Problem 18 17 •Increased atmospheric temperature •Warming of ocean (Increase in heat content) Temperature (° C) Increase in CO2 causes: 16 15 14 13 1860 1880 1900 1920 1940 1960 1980 2000 2020 2040 2060 2080 2100 Y ear Hadley Centre for Climate Prediction and Research
  • Krill in Antarctic Food Webs Phytoplankton
  • Krill Swarms Phytoplankton
  • Antarctic Circumpolar Current (ACC) The West Antarctic Peninsula (WAP) is the location where the ACC is closest to the continent
  • Recent warming in the WAP 2 Qslope (x10 (x109 Heat content 9 J m-2)J m-2) 50-year changes in winter air temperature 9 10 joules per m °C 3.8 3.7 3.6 Seawater heat content 3.5 3.4 3.3 3.2 1992 1994 1996 1998 2000 YEAR 2002 2004 2006 Martinson et al. 2008 Fastest winter warming location on Earth Increase of 6°C in the past 50 years Increase in ocean heat content 87% of glaciers in retreat Sea ice duration decreased by ~90 days Northern WAP perennial ice is gone
  • Warming World The oceans are changing in our lifetime
  • Warming World
  • Warming World
  • Recent changes in WAP phytoplankton • 12% decrease in chlorophyll over past 30 years, particularly northern WAP • Shift from large to small phytoplankton 1970s-1980s 1998-2006 Montes-Hugo et al. 2009
  • Recent changes in WAP Antarctic krill Line 600 (north) Atkinson et al., 2004 • Decrease in Euphausiasuperbaof over twofold per decade since mid1970s
  • Recent changes in Adélie Penguins Line 600 (north) • Decrease in Adélie penguins, increases in subpolar species (Gentoos, Chinstraps)
  • Recent changes in Adélie Penguins Line 600 (north)
  • Increase in CO2 absorption = Increase in ocean acidity
  • Ocean acidification: The “Other” CO2Problem Station Aloha Year Increase in CO2 absorption = Increase in ocean acidity
  • The chemistry of OA: carbonate chemistry Increase in seawater CO2: •Increase in seawater carbonic acid, H2CO3 •Release of hydrogen, H+, ions into the seawater •Decrease pH = increase ocean acidity •Decrease in CO32-ions (buffering process) •Decreased calcification in organisms
  • The chemistry of OA: carbonate chemistry Increase in seawater CO2: •Increase in seawater carbonic acid, H2CO3 •Release of hydrogen, H+, ions into the seawater •Decrease pH = increase ocean acidity •Decrease in CO32-ions (buffering process) •Decreased calcification in organisms
  • The chemistry of OA: carbonate chemistry Increase in seawater CO2: •Increase in seawater carbonic acid, H2CO3 •Release of hydrogen, H+, ions into the seawater •Decrease pH = increase ocean acidity •Decrease in CO32-ions (buffering process) •Decreased calcification in organisms
  • What potential impacts could ocean acidification have on marine organisms and why?
  • Calcification and the Saturation State Ω = potential for the mineral to form or dissolve product of concentrations of reacting ions that form the mineral Ω = Product of the concentrations of those ions when mineral is at equilibrium (Ksp) Ωa > 1: supersaturation of carbonate ions = precipitation Ωa < 1: undersaturated = dissolution
  • Antarctic benthic community Photo: Steve Clabuesch, NSF • • • Rich, diverse, and mostly endemic marine benthic fauna in Antarctica Many benthic calcifying fauna are prominent in nearshore communities and are economically and/or ecologically important (e.g., bivalves, such as mussels and oysters, sea urchins, limpets, brachiopods, cold water corals) Lack of shell-crushing predators: clawed crabs, lobsters, heavily jawed fish
  • Dissolution of multiple Antarctic benthic invertebrates (McClintock et al. 2009) Shell mass7.4 – Shell mass8.2 BIVALVE LIMPET Bivalve Y. eightsishell Control, pH = 8.2 Acidified, pH = 7.4 BRACHIOPOD
  • King crab invasion of Antarctica Photo: Sven Thatje • • • Warming sea temperatures are allowing shell-crushing, deep water king crabs to invade the continental shelves surrounding Antarctica (Thatje et al. 2005) Any additional weakening of invertebrate shells owing to ocean acidification will render them even more vulnerable to these predators. Coupling of rising temperatures, ocean acidification, and predator invasion is expected to influence both planktonic and benthic marine communities of Antarctica
  • Doney et al. 2009
  • What potential impacts could ocean acidification have on NONCALCIFYING marine organisms and why?
  • Effects of ocean acidification on large diatoms • Increased primary productivity • Change in community structure 100 ppmv Tortell et al. 2008 380 ppmv 800 ppmv
  • CO2 Scenarios: Effects on biogeochemistry and food webs High CO2 Large cells Biomass Productivity N, P, Si, Fe uptake Would diatoms ultimately become nutrient limited?
  • Chlor Chlo ** Small**diatoms responded negatively * 0.5 0.5 0.5 0.5 0 Nano(cells mL-1)) Pico (cells mL-1 2 2 * 44 (Saba et al., in prep) 8 10 12 6 6 8 10 12 14 14 7500 7500 30 30 3030 Prim. Prod. (mg C m-3 d-1) Nano (mg mL-1d Prim. Prod.(cellsC m-3 ) -1) 0.0 0.0 0 0 0 25 25 6000 2525 6000 20 20 2020 4500 4500 15 15 1515 3000 3000 10 10 1010 1500 1500 5 5 5 5 0 0 0 0 0 00 0 0 0 0 7500 2000 7500 2000 * * 2 2 22 2 4500 4500 1000 1000 3000 3000 6 8 8 6 6 88 6 8 6 Time (days) Time (days) 10 10 1010 10 12 12 12 12 12 14 14 14 14 14 * * 500 500 1500 1500 2000 2000 * * * 6000 6000 1500 1500 0 0 4 44 44 ** -84% * 0 0 2 2 4 4 * 6 6 8 8 Time (days) 10 10 * * 12 12 -84% -51% 14 14 *p < 0.05 • Lower biomass & productivity in high CO2 treatment • No increase in biomass over course of study
  • Effects on krill embryo development (Kawaguchi et al. 2010) 380 pCO2 (μatm) 2000 pCO2 (μatm)
  • How do you study metabolism?
  • Metabolic physiology: Water breathers rely almost entirely on ion exchange mechanisms to maintain acid-base balance
  • pH/pCO2 effects on metabolic physiology: Water breathers rely almost entirely on ion exchange mechanisms to maintain acid-base balance Pörtneret al. 2004
  • pH effects on brittle star metabolism & growth 8.0 7.7 pH 7.3 6.8 8.0 7.7 pH 7.3 6.8 Wood et al. 2008
  • pH effects on brittle star metabolism & growth 8.0 7.7 pH 7.3 6.8 pH = 8.0 8.0 7.7 pH 7.3 6.8 pH = 6.8 MUSCLE LOSS Wood et al. 2008
  • OA effects on krill metabolism & growth (Saba et al., 2012) FEEDING • Euphausiasuperbaresponded to elevated CO2by: – Increasing ingestion rates
  • OA effects on krill metabolism & growth (Saba et al., 2012) EXCRETION • Euphausiasuperbaresponded to elevated CO2by: – Increasing ingestion rates – Increasing nutrient release rates and metabolic activity • Increased metabolism reflects enhanced energetic requirements of acid-base regulation • Associated compensation costs included the catabolism of proteins
  • OA effects on krill metabolism & growth (Saba et al., 2012) • Euphausiasuperbaresponded to elevated CO2by: – Increasing ingestion rates – Increasing nutrient release rates and metabolic activity • Increased metabolism reflects enhanced energetic requirements of acid-base regulation • Associated compensation costs included the breakdown and loss of proteins
  • Major Findings/Future focus • Many calcifying organisms will be negatively affected by increased ocean acidification
  • Major Findings/Future focus • Many calcifying organisms will be negatively affected by increased ocean acidification • Most detrimental responses of organisms to ocean acidification are in early developmental stages – Potential long-term population declines
  • Major Findings/Future focus • Many calcifying organisms will be negatively affected by increased ocean acidification • Most detrimental responses of organisms to ocean acidification are in early developmental stages – Potential long-term population declines • Little information thus far on non-calcifying organisms and physiological processes (including krill)
  • Major Findings/Future focus • Many calcifying organisms will be negatively affected by increased ocean acidification • Most detrimental responses of organisms to ocean acidification are in early developmental stages – Potential long-term population declines • Little information thus far on non-calcifying organisms and physiological processes (including krill) • Positive effect of ocean acidification on large diatoms – Nutrient limitation may be an eventual problem – Differential responses of different diatoms – Food webs may be altered in ways we do not yet understand
  • Major Findings/Future focus • Many calcifying organisms will be negatively affected by increased ocean acidification • Most detrimental responses of organisms to ocean acidification are in early developmental stages – Potential long-term population declines • Little information thus far on non-calcifying organisms and physiological processes (including krill) • Positive effect of ocean acidification on large diatoms – Nutrient limitation may be an eventual problem – Differential responses of different diatoms – Food webs may be altered in ways we do not yet understand • Multistressorsneed to be considered: CO2, temperature, light, nutrient limitation, oxygen
  • Adaptation of organisms to ocean acidification? CO2 levels were high at times in the geological past without there being much evidence for significant deleterious effects on marine planktonic organisms. That may be because they were slow changes that enabled organisms to evolve to adapt to gradually rising CO2 levels.
  • Adaptation of organisms to ocean acidification? CO2 levels were high at times in the geological past without there being much evidence for significant deleterious effects on marine planktonic organisms. That may be because they were slow changes that enabled organisms to evolve to adapt to gradually rising CO2 levels. Today the rate of rise in CO2 and acidification is 10 times faster than anything experienced since the demise of the dinosaurs 65 million years ago and is closely tied to anthropogenic inputs.
  • Adaptation of organisms to ocean acidification? CO2 levels were high at times in the geological past without there being much evidence for significant deleterious effects on marine planktonic organisms. That may be because they were slow changes that enabled organisms to evolve to adapt to gradually rising CO2 levels. Today the rate of rise in CO2 and acidification is 10 times faster than anything experienced since the demise of the dinosaurs 65 million years ago and is closely tied to anthropogenic inputs. Organisms with prolonged life histories and long generation times (krill, pteropods, fish) will have fewer opportunities for successful acclimation or adaptation to high CO2/low pH seawater.
  • Adaptation of organisms to ocean acidification? CO2 levels were high at times in the geological past without there being much evidence for significant deleterious effects on marine planktonic organisms. That may be because they were slow changes that enabled organisms to evolve to adapt to gradually rising CO2 levels. Today the rate of rise in CO2 and acidification is 10 times faster than anything experienced since the demise of the dinosaurs 65 million years ago and is closely tied to anthropogenic inputs. Organisms with prolonged life histories and long generation times (krill, pteropods, fish) will have fewer opportunities for successful acclimation or adaptation to high CO2/low pH seawater. There will be winners and there will be losers, and these changes will ripple through the food webs
  • Thank you!! Contact info: saba@marine.rutgers.edu
  • Resources for Teachers • WHOI OCB: – http://www.whoi.edu/OCB-OA/ • European Project on Ocean Acidification, EPOCA: – http://www.epoca-project.eu/ • Palmer Long Term Ecological Research datazoo: – http://pal.lternet.edu/outreach/data_zoo.php • Carbon Dioxide Information Analysis Center: – http://cdiac.ornl.gov/ • Carbon Dioxide Research Group, LDEO: – http://www.ldeo.columbia.edu/res/pi/CO2/ • RU COOL, Rutgers Coastal Ocean Observation Lab: – rucool.marine.rutgers.edu
  • Calcification and the Saturation State • Calcite • Aragonite – More soluble  More vulnerable
  • Future Projections – CO2 Emissions 2007 IPCC WG1 AR-4; Projected for end of 21st century
  • Feeley et al., submitted
  • Feeley et al., submitted
  • Marine snails, Pteropods • Shelled pteropods can reach densities of 1000s to 10,000 individuals m-3 in high-latitude areas and comprise up to 25% of total zooplankton biomass in the Southern Ocean • Important prey species for a variety of other zooplankton and fish • Contain a soluble calcium carbonate shell
  • Marine snails, Pteropods • Shelled pteropods can reach densities of 1000s to 10,000 individuals m-3 in high-latitude areas and comprise up to 25% of total zooplankton biomass in the Southern Ocean • Important prey species for a variety of other zooplankton and fish • Contain a soluble calcium carbonate shell (aragonite) UNDERSATURATION SUPERSATURATION Dissolution of Clio pyramidatashell (Orr et al. 2005)
  • Risk map for krill hatching rate (Kawaguchi et al. 2013)
  • Future Projections – Temperature
  • Future Projections – Sea Level Rise
  • Future Projections – Weather Events Scientists predict an increase in the INTENSITY of weather events: hurricanes, precipitation, droughts, coastal flooding
  • Future Projections – Ocean Acidity
  • Recent changes in WAP phytoplankton • 12% decrease in chlorophyll over past 30 years, particularly northern WAP • Shift from large to small phytoplankton # observations (recent – past) # observations (recent – past) 1970s-1980s 1995-2005 Montes-Hugo et al. 2009