Green ice­bergs, also cal­led jade ice­bergs, are rare. Actual­ly so rare that they have some­ti­mes been taken for a cock-and-bull sto­ry. But they do exist. I have seen seve­ral ones mys­elf. So long ago that I have not been able to take pro­per pho­tos, with the stone-age equip­ment that I had back then. So I do not have any pho­tos that show the colour real­ly well. Ok, next time.

Green ice­berg (jade ice­berg) in Brans­field Strait, March 2003. Pho­to taken with pre-his­to­ri­cal equip­ment (dia­film, scan­ned), so not much remains of the beau­tiful ori­gi­nal colour.

But if you have the rare luck to see such an ice­berg, then the green colour is very pro­mi­nent inde­ed. It is not just a hint of green within the usu­al blue of an ice­berg. It is real­ly a dif­fe­rent colour.

The­re has been a lot of spe­cu­la­ti­on regar­ding the reason for the green colour. Accor­ding to the most com­mon theo­ry, the green ice is mari­ne ice: sea­wa­ter fro­zen to the bot­tom of an ice shelf. Not ter­restri­al gla­cier ice, but fro­zen sea­wa­ter. Not fro­zen on the sur­face of the sea, so it is not what is com­mon­ly refer­red to as sea ice. Hence the spe­cial term mari­ne ice. The colour, now, was said to be due to a high con­tent of orga­nic mat­ter of the fro­zen sea­wa­ter. Phy­to­plank­ton trap­ped in the ice.

A team of sci­en­tists (Ste­phen G. War­ren, Col­lin S. Roes­ler, Richard E. Brandt and Mark Cur­ran) have now come up with a new theo­ry which they descri­be in an artic­le published in the Jour­nal of Geo­phy­si­cal Rese­arch: Oce­ans. The good news: not ever­y­thing we pre­vious­ly belie­ved is wrong now. Also this recent publi­ca­ti­on con­firms the mari­ne ori­gin of the ice in ques­ti­on. It is fro­zen sea­wa­ter, fro­zen to the bot­tom of an ice shelf, that is respon­si­ble for the green colour of the jade ice­bergs.

A num­ber of con­di­ti­ons have to be met to enable sea­wa­ter to free­ze to the bot­tom of an ice shelf. This hap­pens at con­sidera­ble depths of seve­ral hundred to more than thousand met­res. And the water has to be very cold. The Ame­ry Ice Shelf in east Ant­ar­c­ti­ca has a groun­ding line depth (whe­re the ice shelf rests on the sea flo­or) of 2400 met­res. The­re, the free­zing point of sea water is -3.7°C. If this water hap­pens to move to hig­her levels under the ice shelf, then it is super­coo­led.

Green ice­berg (jade ice­berg) near the South Ork­ney Islands, Janu­ary 2009. The mari­ne ice has for­med within cracks at the bot­tom of the ice shelf, which gives the green ice the appearance of being work­ed into the blu­eish-white, ter­restri­al gla­cier ice.

The dif­fe­rence to older theo­ries is the ques­ti­on of what in the sea­wa­ter exact­ly brings the green colour. War­ren and his col­le­agues cla­im that the sub­s­tance in ques­ti­on is not orga­nic, but iron com­pounds. Mea­su­re­ments of an ice core from the Ame­ry Ice Shelf that includes basal sec­tions of mari­ne ice do not show high con­cen­tra­ti­ons of orga­nic mat­ter. Ins­tead, the iron con­tent was hig­her than expec­ted.

The iron is part of various che­mi­cal com­pounds, but altog­e­ther of anor­ga­nic ori­gin. The main mine­ral is Goe­thi­te, an iron-bea­ring hydr­o­xi­de which is a com­mon mine­ral in the upper crust. The source is rock mate­ri­al ero­ded at the gla­cier base.

The opti­cal pro­per­ties (absorp­ti­on spec­tra) of Goe­thi­te dust tend to give a yel­lo­wish colou­ra­ti­on. But the inter­play of this brow­nish-yel­lo­wish colour with the blue of den­se (wit­hout air bubbles) sea ice can pro­du­ce exact­ly the jade-colour in ques­ti­on.

Com­plex mat­ter! Not sur­pri­sin­gly, the aut­hors of the stu­dy con­clude that fur­ther rese­arch is nee­ded: regar­ding the exact com­po­si­ti­on of orga­nic (and anor­ga­nic) sub­s­tances mixed with mari­ne ice and their opti­cal cha­rac­te­ristics. Final­ly, such know­ledge might be used to gain infor­ma­ti­on about the che­mi­cal com­po­si­ti­on of ice­bergs from light spec­tra that can be mea­su­red effi­ci­ent­ly by remo­te sens­ing, using air­craft or dro­nes or even satel­li­tes.

And the che­mi­cal com­po­si­ti­on of ice­bergs, espe­ci­al­ly the iron con­tent, is actual­ly very important for the mari­ne eco­lo­gy of the Sou­thern Oce­an: mine­rals trans­por­ted by ice­bergs can fer­ti­li­se sea­wa­ter that is other­wi­se poor in such nut­ri­ents. Such fer­ti­li­sa­ti­on can have signi­fi­cant effects on the bio­lo­gi­cal pro­duc­ti­vi­ty of the oce­an. Hence, the beau­tiful “jade ice­bergs” gain unex­pec­ted importance for the eco­lo­gi­cal sys­tem of the Sou­thern Oce­an.

The volu­me of green ice is pro­ba­b­ly lar­ger than one might belie­ve, con­side­ring the rari­ty of green ice­bergs. But only smal­ler ice­bergs are actual­ly able to turn over, expo­sing the green bot­tom. Lar­ger tabu­lar ice­bergs may trans­port much grea­ter quan­ti­ties of green ice but this remains then hid­den at gre­at depth. And of cour­se the light has to be right to see it and you have to bee around … and not every ice shelf pro­du­ces jade ice­bergs in quan­ti­ties. The Ame­ry Ice Shelf is so remo­te that peo­p­le hard­ly every get the­re, other than sci­en­tists who work on the sta­ti­ons Maw­son and Davis (both belong to the Aus­tra­li­an Ant­ar­c­tic Divi­si­on).

So, if you have every seen a green ice­berg in rea­li­ty, then you are one of a lucky few!

Tho­se who have the pri­vi­le­ge to have seen South Geor­gia with their own eyes will remem­ber the island as a wild­life para­di­se. Seals, pen­gu­ins, fly­ing sea­birds – they are all the­re. The colo­nies are huge­ly impres­si­ve.

And the­re have been good news about the con­ser­va­ti­on sta­tus of South Geor­gia in recent years. The reinde­er that Nor­we­gi­an wha­lers had intro­du­ced from 1911 were cul­led until 2014. In South Geor­gia, the reinde­er popu­la­ti­on had a den­si­ty of up to 85 ani­mals per squa­re kilo­met­re, in con­trast to about 5 per sq km in Spits­ber­gen. It does not sur­pri­se that the vege­ta­ti­on in South Geor­gia suf­fe­r­ed sever­ely from the con­stant tram­pling and gra­zing from thou­sands for reinde­er in tho­se are­as whe­re they exis­ted. This was evi­dent when you com­pared tho­se parts of South Geor­gia whe­re reinde­er roa­med the tus­sock grass with other are­as whe­re they never exis­ted. The era­di­ca­ti­on pro­ject gai­ned prio­ri­ty when the ongo­ing retre­at of gla­ciers threa­ten­ed to enable reinde­er to migra­te to other parts of the island which had been natu­ral­ly clo­sed of until now. Whe­re­ver pos­si­ble, reinde­er were her­ded and slaugh­te­red; else­whe­re, they were shot by hun­ters. The last ones were cul­led in 2014. Sin­ce then, the vege­ta­ti­on and accor­din­gly many bird spe­ci­es asso­cia­ted with the tus­sock gras com­mu­ni­ties can return to their ori­gi­nal habi­tat in tho­se are­as form­er­ly inha­bi­ted by reinde­er.

A view from the past: Reinde­er on South Geor­gia (St. Andrews Bay, 2009).

Get­ting rid of rats was ano­ther and much lar­ger chall­enge. The­se came also with the wha­lers to the island. They thri­ved soon in many are­as – a dis­as­ter for many ground-bree­ding sea­birds, mea­ning pret­ty much all of them (the­re are no trees on South Geor­gia). Rats take eggs and chicks from nests and bur­rows and they don’t even hesi­ta­te to have a go at chicks from lar­ge alba­tros­ses.

In a her­cu­lean effort that las­tet over seve­ral years, the South Geor­gia Heri­ta­ge Trust has era­di­ca­ted rats on South Geor­gia. The eva­lua­ti­on pha­se is still going on, but years of moni­to­ring have not shown any traces of rats still being pre­sent on the island. Birds such as the South Geor­gia pipit which had been rest­ric­ted to small off-lying islands for many deca­des soon star­ted to re-estab­lish them­sel­ves on the main island.

The reco­very of wha­le and seal popu­la­ti­ons after cen­tu­ries of inten­se cat­ching and hun­ting is also good news. Today, thou­sands of Fur seals crowd South Georgia’s bea­ches again. Some wha­le spe­ci­es will need cen­tu­ries to return to pre-indus­tri­al levels if they ever do, while others, noti­ce­ab­ly the Hump­back wha­le, make a swif­ter return. The over­all deve­lo­p­ment is posi­ti­ve.

But all the­se good news and suc­ces­ses don’t mean that ever­y­thing is as it should be. Bycatch in fishe­ries has been an issue for deca­des, being the reason for dra­ma­tic decli­nes of many sea­bird spe­ci­es not only in South Geor­gia, but in many are­as of the world. This includes ico­nic spe­ci­es such as the Wan­de­ring alba­tross and many of its clo­se rela­ti­ves. Also here, the­re have been regio­nal impro­ve­ments: in South Georgia’s waters, strict regu­la­ti­ons have brought major impro­ve­ments. Here, bycatch does not have a signi­fi­cant effect on popu­la­ti­ons any­mo­re, birds drow­ning on longli­nes are rare excep­ti­ons today. That is the good news. The bad news is that fishing ves­sels else­whe­re in the Sou­thern Oce­an (or else­whe­re, for that sake) ope­ra­te under much less strict regu­la­ti­ons and often ille­gal­ly. And many sea­birds tra­vel thou­sands of miles on their fora­ging trips. Regio­nal pro­tec­tion will not be able sol­ve the pro­blem.

As a result, in spi­te of regio­nal suc­ces­ses bycatch is still con­side­red the one big main thre­at for many sea­bird popu­la­ti­ons. Also on South Geor­gia, seve­ral alba­tross spe­ci­es are still decli­ning stron­gly – in a sta­te which is alre­a­dy con­side­red any­thing but sta­ble and healt­hy. Spe­ci­es inclu­ding Wan­de­ring, Black-bro­wed and Grey-hea­ded alba­tross are all lis­ted on the IUCN list at various levels of risk. And all of them are still losing indi­vi­du­als at an alar­ming rate, as is con­firm­ed by recent sur­veys..

Wan­de­ring alba­tross on nest on Bird Island, South Geor­gia.

The num­ber of Wan­de­ring alba­tros­ses bree­ding on South Geor­gia has decli­ned by 18 % in just 11 years, from 2003/04 to 2014/15. Spea­king in abso­lu­te figu­res, only 1278 were left out of 1553 in the begin­ning of the abo­ve-men­tio­ned peri­od. Black-bro­wed alba­tros­ses went through a very simi­lar deve­lo­p­ment with a loss of 19 %. For Grey-hea­ded alba­tros­ses, the situa­ti­on was even much more dra­ma­tic with a loss of a stun­ning 43 %.

And it is not that this deve­lo­p­ment star­ted at a healt­hy level in 2003/04. Popu­la­ti­ons have decli­ned at least sin­ce the 1970, when sci­en­tists star­ted to moni­tor them more regu­lar­ly. Today’s colo­nies are just a shadow of what they were when South Geor­gia and the Sou­thern Oce­an were still untouch­ed by man, befo­re wha­ling and seal­ing star­ted. Sal­ly Pon­cet and her co-aut­hors con­sider bycatch in fishe­ries still the main thre­at for South Georgia’s alba­tros­ses.