POTENTIAL IMPACTS OF CLIMATIC CHANGE ON THE SOUTHERN OCEAN ECOSYSTEM RG.CHITTLEBOROUGH Chittteborough. R.G. 1991 07 01; Potential impacts of climatic change on the Southern ocean ecosystem. Memoirs ofthe Queensland Museum 30(2);243-247. Brisbane. ISSN Q079-8835. Globalclimatechange has the potential todisrupt the delicately poised thermal balance in surfacewatersoftheSouthernOceanaroundAntarctica,threateningthishighly productive ecus\stem aith severeand permanent collapse. Pivotal in this process is a diminution pf the important (but lilile studied) CO: sink in the Southern Ocean, resulting in a seriesof feedback loops accelerating global warming and intensifying impacts upon the Southern Oceanecosystem. As well as outlining the processes involved and stressing the urgent need for further research, this paperunderlines cur wider social responsibilities to press for fresh policies essential to arrest the global changes before irreversible harm is done to the Antarctic environmentand ecosystems, wfth 'heirglobal consequences toour lifesupport system. R.G. Chittleborough, 24 WattSt. Swanbourne WesternAustralia 6010;4January 1991. TheConvention forConservationofAntarctic annual pulse of winter sea ice extending Marine Living Resources, (CCAMLR), while northwards from Antarctica to cover some 20 "RECOGNISING the importance ofsafeguard- million square kilometres of the Southern ing the environmentand protecting the integrity Ocean, retreating each summer almost to the Of the ecosystem of the seas surrounding An- mainland coast. This annual pulse drives the tarctica"; places its main emphasis on the im- vertical circulation ofthese waters (Fig. IK cold pacts which harvesting may have, notonly upon brine releasedbytheformationofseaicesinking target species but also upon ecological relation- along the continental shelf, with compensatory ships. Article II ofthe Convention also commits upwellingofnutrient rich waterfartheroffshore us to the conservation principle of "prevention at the Antarctic Divergence (Sverdrup et ofchangesorminimisationoftheriskofchanges a/.,1942). Microalgae growing from the base of in the marine ecosystem which are notpotential- the sea ice, and phytoplankton blooms each ly reversible over twoor three decades...?? spring and summer within the nutrient rich An- However, even ifthere was no exploitation of tarctic Surface Water, arc the main basis of the iving(ormineral)resourcesin the Antarctic,the high productivityofthe Southern Oceanecosys- I environment and ecosystems there are now tem (Chittleborough. 1984). Estimates of gross threatened by accelerating climatic changes annual production of phytoplankton are 6,1-38 being triggered globally by mankind. billion tonnes. This representsan annual uptake Not surprisingly, the main focus of attention of 1.5-10billion tonnesofCO:. Partofthat CO: presently being given to global climatic change is released again during metabolic activity of is how thechangeswill impactonourselves. We consumers, but a proportion sinks as detriiai have begun to consider how quickly we may organiccarbon into Antarctic Bottom Water. have to adapt in terms ofwater supply, agricul- Some dissolved CO: from the atmosphere i*. ture, forestry, transport, coastal developments, also carried down in both the Antarctic Bottom etc. Fat less attention isbeinggiven to potential Water and the Antarctic Intermediate Water impacts upon natural ecosystems, particularly sinking at the Antarctic Covergence. the more remote Antarcticecosystem. While it is widely accepted that the Southern Ocean is a major sink for CO: measurements of PROCESSES MAINTAINING THE the sink are not available. Takahashi (1987) es- SOUTHERN OCEAN ECOSYSTEM timated that the Southern Ocean removes 6,67 billion tonnes of CO: per year from the atmos- The main driving force of this system is the phereor 70% oftotal uptake flux ofall oceans. 244 MEMOIRS OFTHEQUEENSLAND MUSEUM Fig. 1, Representation ofcurrents and water massesoi theAntarcticregions (afterSvenirupetal., 1942). THERMALSTABILITY summer, as this is the time ofgreatest shipping activity in the Southern Ocean. While much of The advent ofsatellite sensing affords a prac- thisinformation isstill tobecollated, ananalysis tical means ofassessing long term variations in by Bcntley (1984) indicatesthat the extentofthe thermal stability of the Southern Ocean. Jacka Antarctic sea ice in summer decreased by 2.5 (1983)stressedthe importanceofmonitoringthe million square kilometres between 1973 and extent of winter sea ice, as this parameter is 1980, and perhaps by more since the 1930*s. likely to be one of the earliest indicators ofany There is evidence of a recent increase in air significant climatic change. temperature over the Southern Ocean. Budd Assatelliteimagesofthewinterseaicearound (1980) recorded an increase in mean annual air Antarctica became available, extensive open temperature at subantarctic islands of 0.4° C waters within the ice (polynyas) were dis- during 1958-1978 and by 0.6° C at stations on covered. The largest of these, the "Weddell the edge of the Antarctic continent. At Ker- Polynya" (actually situated to the east of the guelen Island, situated on the northern edge of Weddell Sea) measured 1 100 x 650 km in Sep- Antarctic Surface Water, the mean annual air tember 1975. The Weddell Polynya appeared in temperature has risen during 1964-1982 by 2.1p three consecutive winters. L974—1976, then dis- C (Jacka. Christou & Cook, 1986). the increase appeared until 1980 (Corniso and Gordon. being more marked in summer than in winter. !987), Farther cast at c. 45:£, the Cosmonaut Similar rises in mean annual air temperature are Polynya appeared in 1973,1975, 1979,1982 and recorded for Amsterdam Island and Marion Is- 1986. While it is not suggested that these land. polynyas were caused by the greenhouse effect, On glaciated subantarctic islands such as they do serve to illustrate the delicate balance in Heard Island, glacial retreat has accelerated the formation and maintenance ofsea ice. dramatically in recent decades (Allison and Rather more information is available on the Kxage. 1986). Heard Island, located towards the extent and distribution ofresidual sea ice during outer marginofAntarcticSurface Water,and its CLIMATICCHANGE INTHE SOUTHERN OCEAN ECOSYSTEM glaciers moving rapidly on steep slopes (short important component of primary production residence time of ihc ice), affords sensitive in- duringwinterandearlyspring), and lessice floes dicators ofchanges in elimale suitable, for pupping and mating of ice seals While there is a paucity of hard data on (particularly crabcatcr and leopard seals) at the Variability within the Southern Ocean region, it critical period during late October and early- is evident from the great changes occurring November each year. seasonally and in the longer term, that the ther- One of the physical effects of a reduction in mal balance ofthis region is delicately poised. the extent of sea ice would be a less of ulK and further absorption of solar energy into the POTENTIAL FORCHANGE surface ofthe Southern Ocean, accelerating the change in the energy balance. Global climate models used to predictsurface An even more important feedback loop from airtemperaturechangesduetoincreasingatmos- a much reduced extent of winter sea ice would pheric CO2,generally indicate greater increases be a severe reduction in the pulse driving the tn temperature at Inghei latitudes. For example, VCtlical circulationOfthe watersofthe Southern Rind (1984) indicated that a doubling ofatmos- Ocean. Withlesssea ice formed, there wouldhe pheric CO: would raise mean annua! .. less brine released to sink us Antarctic Bottom temperatures over most of Australia by 4+-°C, Wfttei and tience diminution of the passage ol while over the Southern Ocean around An- dissolved CO2 to be held in the deepocean sink. tarctica increases of6-8cC could be anticipated With the weakening of the vertical circulation Sea surface temperatures in the Southern Ocean there would also be a decline in compensatn-s can therefore be expected to rise by a greater upwclling of nutrient rich water upon which amount than in lower latitudes. phyloplankton and all higher consumers are to- The most immediateeffectofSouthernOcean tally dependent. A failure of phytoplankion surface isothermscon raeiingsouihwjudswould blooms would represent a massive rrditciior m 1 be to further restrict the distribution of cold the fixation of COa in Antarctic Surface Water, lolerani species living within Antarctic Surface againfeedingback toaccelerateglobal warm Water. For example, most of Ihc slock ol A severe reduction in primary production tuphuusta supr-r' ifined to waters less within Antarctic Surface Water would have a than :CC(Marr, 1962). wrule E. crystallorophias disastrousimpactontheSouthernOceaneco Btfictfid towatersofeven lowertemperature. tern as a whole, including the harvested species The shrinking range of such key food species which CCAMLR is attempting to manage and will compress dependent consumerspecies into conserve. Furthermore, a diminution of krill a narrower band around Antarctica, increasing Stocks through man-induced climate char competition between predators. Around some would severely retard (or reverse) the recovejry sub-Anlarctic island^ vital food resources may of previously depleted populations of blue, fin then he beyond the foragingrange ofadult seals and humpback whales, negating much of the and birdsduring the critical period ofrearing the hard-won ground bv the IW( '. young. Croxal ct aJ. (W87) showed that this Furtherpotentialforimpactuponthe Southern already occurs sporadically at South Georgia. Ocean ecosystem derives from the ultra', 1 Om ofthe mO$l Tar reaching effects of rising wavelengthspenetratingtheozone holenowevi- sea surface temperatures in the Southern Ocean dent in the stratosphere over Antarctica each Would be aprogressive reduction in theextentof springand early summer. Increasingpenetration sea ice, both in winter and summer. In an initial of L'V biind into the sea surface has potential to modellingofthe potential impactupon Southern depressphotosynthesisoreven to be lethal 10the Ocean sea ice. Parkinson and Bindscnadlcr more sensitive species in the phytoplankion. (1984) concluded that a rise of 5°C in ait again depressing the productivity of rh6 WO temperaturecould result in the WlnteJ MMM and tern as well as reducing the uptake of atmos- volume ofsea ice to be halved. As the increase pheric COa Precis field measurements arc 1 ir temperature at high latitudes is anticipated lacking, but Pittock cl al. (I98l) suggested thai to continue to rise well beyond thai level, the phyloplankton in surface waters would suffer svinter extent o\ sea ice could be reduced even appreciablemortalitybyareductionoftheozone further shield in the range of 16-39%. In October I Direct ecological impactsofareduction msea ozone levels over Antarctica declined by include loss of -substrate tor ice algae 1 *fl (Embei e| hl*i 19Rfi) Concentrations of 246 MEMOIRS OFTHE QUEENSLAND MUSEUM Excessive resource consumption ^. Warmer X Less southern Lower Antarctic ocean albedo sea-ice &- Greenhousegases Less h< Ozonehole accumulatein { krill Lesspenguins instratosphere troposphere lessseals overAntarctica /\ lesswhales Eyedamage tonew-bom H Less seals&birds> Wanner dceatrribtoanl & troposphere •UV(B) penetrates surfacewater Less Antarctic Less bottomwater upwelling ofnutrients Fasterrise Muchreduced inatmospheric oceansink CO2 ofC02 Fig. 2. Potential feedbackloopswithin the Southern Ocean ecosystem resultingfrom climaticchanges. phytoplankton some tens of metres below the toaffectglobalclimatechange,arenotdiscussed surface may be afforded some protection from here. These include acceleration of break-up UV radiation, but turbulent wind mixing bring- fromthefringesoftheAntarcticglacialicesheet, ingthese organismsclose tothe seasurface may and a weakening circulation of the Southern well make them more vulnerable. Ocean triggering a permanent ENSO phen- Of more immediate impact could be the eye omenon. As stressed by Thomas (1984) "we damage that the UV band might bring to new- cannot rule out the possibility that a climate bornsealsandbirds. Particularlyvulnerablehere changeofmagnitudepredictedforCO2doubling wouldbe thepupsofcrabeaterseals, bornon ice could radically alter ocean circulation". In par- floes in high latitudes late in October, close to ticular,hepointsoutthatiftherelativelywarmer the peak ofthe ozone hole. Again, direct meas- Circumpolar Deep Water is able to reach the urements ofsensitivity are lacking. major ice shelves without considerable cooling, There are many potential feedback loops im- ice shelves could thin enough for massively en- pacting on the Southern Ocean ecosystem from hanced calving. "Clearly", he concluded, "we global warming and weakening of the ozone need to learn more about ocean behaviour near shield (Fig.2). Even ifsubsequentresearch finds Antarctica." thatoneortwooftheseprocessesareofrelative- ly minor extent, the overall prognosis for the CONCLUSION Southern Ocean ecosystem is extremely poor. Furthermore, the collapse of the important There can be little doubt that the Southern Southern Ocean CO2 sink has global implica- Ocean ecosystem is threatened with severe and tions, greatly accelerating the rates of climate permanent collapse as a result of impending change that each ofus will have to face. climaticchanges. Such acollapsewould haltthe Itshouldbenotedthatotherfeedbacksystems present recovery of humpback whale popula- in the Antarctic, not directly relating to the tions. Southern Oceanecosystem,buthavingpotential As scientists, we can design fascinating CLIMATICCHANGE IN THE SOUTHERN OCBAN BCOSYSTI M studies of the physical and biological impacts Environmental Studies. ANU Mon. 11: 135- upon the Antarctic environment as global 161. climatic changes progress. But do we not also COMISO, J.C. AND GORDON, AL. 1987. Recur- have a wider responsibility to press for policy ring polynyas over the Cosmonaut Sea and changes aimed at arresting the global processes Maud Rise..l. Geophys Res,92: 2819-2833. before irreversible harm is done to the Antarctic CROXALL J.P. el at 1987. Reproductive perfor- environment and ecosystems Although ii is manceofseabirdsandsealsatSouthGeorgiaand quite evident that we need far more research in SignyIsland,SouthOrkneyIslands. 197h-19S7; this area, we can hardly afford to regard the implications for Southern Ocean monitoring Southern Ocean as a giant experimental unit if studies. SC-CAMLR.SelectedScientificPapers wc are likely to lose control ofthe experiment. 1987:445-447, Ourroleshould befar more than the gathering EMBER, L.R. et al. 1986. Tending global commons. ofinformation.Wewouldbe failing in oursocia! Chemical & Engineering News 64 (47): 14-64. responsibilities ifwe do not make a clear state- JACKA, T.H. 1983. A computer data base for An- menton the urgent needforaction tocircumvent tarctic sea ice extent. ANARE Research Nines the setting up in the Southern Ocean of irre- 13: 1-54. versibleprocesseshavinghigh potential tocause JACKA. T.H.. CHRLSTOU, L. AND COOK, B.F. massive environmental and ecological changes 1984. A databankofmean monthly and annual around Antarctica, as well as greatly accelerat- surface temperatures for Antarctica, the ingchanges inclimate(andsea level)throughout Southern Ocean and South Pacific Ocean, the world. ANARE Research Notes22: 1-97. Unless we act quickly and decisively, the MARR, J.W.S. 1962. The natural history and geog- conservation strategies presently being pursued raphy ofthe Antarctic krill (F.uphausiasuperba by Australia within the IWC CCAMLR andthe Dana). Discovery Reports 32: 37-465- AntarcticTreatyitself,becomemeaninglessges- PARKINSON. C.L AND BINDSCHADLER. R.A. tures. As stated recently by Dr Noel Brown of 1984. Response ofAntarctic sea ice to uniform UNEP, the next decade is our last window of atmospheric increases. Geophysical Mono- opportunity tomake effectivechanges. Let'suse graphs 29: 254-264. that time to the full. PITTOCX A.B. et al. 1981. Human impact on the globalatmosphere impactstorAustralia.Search LITERATURECITED 12: 2h(i-2^: RIND, D 1984. Global climate in the 21sL Century. ALLISON, IF AND KEAGE, P.L. 1986. Recent Ambio 13: 148-151. changes in the glaciers of Heard Island Polar SVERDRUP,H.V etat. 1942."Theoceans'.(Prentice Record 23 (144); 255-271. hall: N.Y). BENTLEY. C.R. 1984. Some aspects of the cryo- TAKAHASHI, T. 1987. Assessment ofseasonal and sphereanditsrole inclimaticchange.Geophysi- geographicvariability in CO2sinksandsources cal Monographs 29; 207-220. in the ocean. In Reichle, D.E el al , Environ- BUDD, W.F. 1980. The importance of the polar mental Sciences Div. Ann. Progr, Rep. for regions forthe atmospheric carbon dioxidecon- period ending Sept. 30 1986'. 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