Advanced search
1 file | 14.25 MB Add to list

Influence of climate change on the postglacial evolution of Patagonian glaciers and response of the solid earth

Matthias Troch (UGent)
(2023)
Author
Promoter
(UGent) and (UGent)
Organization
Project
Abstract
Over the last decades, global warming has caused widespread shrinking of the cryosphere, with two thirds of glaciers worldwide (excluding the Greenland and Antarctic ice sheets) projected to disappear by 2100 CE. Large uncertainties however remain in maritime settings, where some glaciers have recently gained mass in response to increased snowfall or lowered air temperatures related to changes in atmospheric circulation. In addition, worldwide ice-mass loss has caused sea level to rise on a global scale. On a local scale, however, sea level has fallen in glacierized regions due to Glacial Isostatic Adjustment (GIA) of the underlying solid earth related to decreasing ice loads. On these two aspects, Patagonia stands out. Increased precipitation along the western side of the Andean ice divide since the 1980s, for instance, has partly attenuated ice mass loss in response to atmospheric warming. In addition, this region is home to the largest glacial isostatic rebound rate ever recorded, with recent GPS measurements revealing crustal uplift rates exceeding 4 cm/year. Detailed analyses of past glacier-climate and glacier-isostasy interactions in Patagonia are needed to better assess how future climate change will affect both the local cryo- and lithosphere. Given the location of the Patagonian icefields at the warm end of the continuum of climatic and oceanographic settings at which glaciers reach sea level, conducting research on Patagonian outlet glaciers might also provide us with a crucial window into the future of similar glacierized regions across the world. With this in mind, the goal of this thesis is to better comprehend how Patagonian outlet glaciers along the maritime side of the southern Andes responded to climate change over the past millennia, and to quantify the magnitude and rate of the associated isostatic response. More specifically, we aim to address two research questions: (1) “What is the relative importance of temperature and precipitation on glacier variability along the humid side of the southern Andes?”, and (2) “How fast and how much did the solid earth respond to post-Last Glacial Maximum ice load changes?”. To answer the first research question, the postglacial fluctuations of three outlet glaciers located along the hyperhumid western side of the Southern Patagonian Icefield were reconstructed using a multi proxy analysis of a sediment core collected in a proglacial fjord. Our results show that the investigated glaciers retreated into their respective fjords by 11.2 cal kyr BP, and remained relatively stable during the first half of the Holocene. Thereafter, they fluctuated considerably during the Neoglacial period, with four marked episodes of glacier shrinkage at 5.8 – 4.8, 3.9 – 2.4, 1.0 – 0.2 cal kyr BP, and during the 20th century. Furthermore, our analysis of sediment cores collected along the fjord–shelf–slope continuum connecting Patagonia with the Pacific Ocean confirms that fjord sediment cores collected within 40 to 60 km from the present-day ice front, such as the core analyzed in this thesis, are ideally suited to reconstruct glacier fluctuations over the entire Holocene. Although sediment cores located further offshore are necessary to reconstruct pre-Holocene glacier variability, those sites are not sensitive enough to Holocene glacier fluctuations. In addition, the comparison of our sediment record with geological archives from both sides of the Patagonian icefields (46° – 56°S) suggests synchronous glacier variability on multi-centennial timescales during the Neoglacial period, which implies a regional climate control. The response of the same three outlet glaciers to changes in air temperature and precipitation during the Neoglacial period was simulated using a numerical ice-flow model. Our experiments show that, on weighted average, precipitation drove 67% of the centennial-scale fluctuations in glacier volume over the last 6000 years. When applied to the temperature projected for the end of this century, our data-validated numerical model indicates that precipitation increases of 10 – 50% are needed to stabilize the investigated glaciers, depending on the climate scenario (SSP1-2.6 to SSP5-8.5). This implies that if future emissions of greenhouse gases are curtailed and the Paris agreement fulfilled, there is a chance that even a modest increase in precipitation can stop mass loss of some of Patagonia’s largest glaciers. On the other hand, if greenhouse-gas emissions follow one of the least optimistic scenarios, it is unlikely that precipitation will increase sufficiently to avoid further temperature-induced ice-mass loss. To answer the second research question, the magnitude and rate of GIA near the center of the former Patagonian Ice Sheet during the Late Glacial and Holocene was reconstructed through a multi-proxy analysis of a sediment core collected in a previously marine-isolated bay. Our results indicate that glacial isostatic rebound started before 16.5 cal kyr BP and that it outpaced global sea-level rise until slightly before 9.1 cal kyr BP. Between 16.5 – 9.1 cal kyr BP, the center of the former Patagonian Ice Sheet rose ca. 96 m, at an average rate of 1.3 cm/year. Glacial isostatic rebound continued (ca. 20 m) over the last 9.1 kyr, but at a slower average pace of 0.2 cm/year. Our data furthermore suggest that the GIA rate fluctuated considerably within these time intervals, in response to glacier dynamics. More specifically, most of the GIA registered between 16.5 – 9.1 cal kyr BP seems to have occurred before meltwater pulse 1A (14.5 – 14.0 kyr BP). During most of the last 9.1 kyr, GIA remained relatively slow, but accelerated during the late Holocene in response to Neoglacial ice load changes. Overall, our analysis of GIA near the center of the former Patagonian Ice Sheet implies a relatively rapid response of the local solid earth to ice unloading, which is in agreement with independent modelling studies investigating contemporary uplift. We conclude that the center of the former Patagonian Ice Sheet experienced a GIA of ca. 116 m over the last 16.5 kyr, and that >80% occurred during the Late Glacial and early Holocene. Overall, our findings have important implications for the glaciological future of Patagonia. First, current regional climate projections indicate that if we continue to follow the most aggressive greenhouse gas emission scenario (RCP8.5), the possible increase in precipitation will most likely be insufficient to counter further temperature-induced glacier decline. Important to note, however, is the low confidence of the forecasted precipitation changes under RCP8.5 due to the complex interaction of the Andes with the humid westerly winds, which highlights the urgency to develop local models able to provide accurate and precise forecasts of precipitation change. Second, rapid glacial isostatic rebound will most certainly continue over the coming decades, but how rebound rates will evolve in the future will strongly depend on precipitation. In addition, this glacial isostatic rebound may indirectly stabilize marine-terminating glaciers to some degree, however, this stabilizing mechanism will likely be countered by future glacier thinning, which appears inevitable under RCP8.5. Overall, this thesis has shown that precipitation plays a more important role than temperature in controlling centennial-scale glacier fluctuations in western Patagonia, and by extension in other maritime regions, and that the solid earth had a particularly rapid response to both deglacial and Neoglacial ice-load changes.
Over de afgelopen decennia heeft de opwarming van de aarde geleid tot een globale inkrimping van de cryosfeer, waarbij naar verwachting tweederde van de gletsjers wereldwijd (met uitzondering van de Groenlandse en Antarctische ijskappen) tegen het jaar 2100 CE zal zijn verdwenen. Er blijven echter grote onzekerheden bestaan in maritieme omgevingen, waar sommige gletsjers recent aan ijsmassa hebben gewonnen als reactie op meer sneeuwval of lagere luchttemperaturen door veranderingen in de atmosferische circulatie. Daarnaast heeft het wereldwijde verlies aan ijsmassa geleid tot een globale stijging van de zeespiegel. Op lokale schaal is het zeeniveau in gebieden met gletsjers echter gedaald door de Glaciale Isostatische Aanpassing (GIA) van de onderliggende vaste aarde ten gevolge van afnemende ijsbelasting. Wat deze twee aspecten betreft, valt Patagonië uitermate op. Zo heeft de toegenomen neerslag langs de westkant van het Andes gebergte sinds de jaren 1980 het verlies van ijsmassa als reactie op de opwarming van de atmosfeer gedeeltelijk gecompenseerd. Daarnaast kent deze regio de grootste geobserveerde glaciale isostatische opveringssnelheid (4 cm per jaar) volgens recente GPS-metingen. Gedetailleerde analyses van de interacties tussen gletsjers en klimaat en tussen gletsjers en isostasie in Patagonië uit het verleden zijn cruciaal om beter te kunnen beoordelen hoe toekomstige klimaatveranderingen zowel de lokale cryo- als lithosfeer zullen beïnvloeden. Gezien de ligging van de Patagonische ijsvelden aan het warme uiteinde van het continuüm van klimatologische en oceanografische omstandigheden waarbij gletsjers het zeeniveau bereiken, levert onderzoek naar de evolutie van Patagonische gletsjers ons een cruciaal beeld op de toekomst van soortgelijke glaciale regio's over de hele wereld. Met dit in gedachten is het doel van deze thesis om beter te begrijpen hoe Patagonische gletsjers langs de westelijke, maritieme kant van de zuidelijke Andes hebben gereageerd op klimaatveranderingen in de afgelopen millennia, en om de omvang en snelheid van de bijbehorende isostatische aanpassingen te kwantificeren. Meer specifiek richten we ons op twee onderzoeksvragen: (1) "Wat is het relatieve belang van luchttemperatuur en neerslag op de gletsjervariabiliteit langs de maritieme kant van de zuidelijke Andes?", en (2) "Hoe snel en hoeveel heeft de vaste aarde gereageerd op veranderingen in de ijsbelasting na het Laatste Glaciale Maximum?". Om de eerste onderzoeksvraag te beantwoorden werden de postglaciale fluctuaties van drie gletsjers langs de maritieme westkant van het Zuidelijke Patagonische ijsveld gereconstrueerd met behulp van een multi-proxy analyse van een sedimentkern die verzameld werd in een proglaciale fjord. Onze resultaten tonen aan dat de onderzochte gletsjers zich tegen 11,2 cal. kyr BP terugtrokken in hun respectievelijke fjorden en relatief stabiel bleven gedurende de eerste helft van het Holoceen. Daarna fluctueerden ze aanzienlijk tijdens het Neoglaciaal, met vier duidelijke episodes van gletsjerkrimp op 5,8 – 4,8, 3,9 – 2,4, 1,0 – 0,2 cal. kyr BP, en tijdens de 20e eeuw. Daarnaast bevestigt onze analyse van sedimentkernen die verzameld zijn langs het fjord – continentaal plat – continentale helling continuüm dat Patagonië met de Stille Oceaan verbindt, dat sedimentkernen uit fjorden die verzameld zijn binnen 40 tot 60 km van het huidige ijsfront, zoals de kern die in deze thesis werd geanalyseerd, bij uitstek geschikt zijn om gletsjerfluctuaties over het hele Holoceen te reconstrueren. Hoewel sedimentkernen die verder van de kust liggen nodig zijn om pre-Holocene gletsjervariabiliteit te reconstrueren, zijn deze locaties niet gevoelig genoeg voor Holocene gletsjerfluctuaties. Bovendien suggereert de vergelijking van ons sedimentarchief met geologische archieven aan beide zijden van de Patagonische ijsvelden (46° – 56° zuiderbreedte) een synchrone gletsjervariabiliteit op tijdschalen van meerdere eeuwen tijdens het Neoglaciaal, wat een regionale klimaatcontrole impliceert. De reactie van dezelfde drie gletsjers op veranderingen in luchttemperatuur en neerslag tijdens het Neoglaciaal werd gesimuleerd met behulp van een numeriek gletsjermodel. Onze experimenten laten zien dat neerslag gemiddeld 67% van de schommelingen op honderdjarige schaal in het gletsjervolume over de afgelopen 6000 jaar heeft veroorzaakt. Toegepast op de temperatuur die voor het einde van deze eeuw wordt verwacht, geeft ons numerieke model aan dat een neerslagtoename van 10 – 50% nodig is om de onderzochte gletsjers te stabiliseren, afhankelijk van het klimaatscenario (SSP1-2.6 tot SSP5-8.5). Dit betekent dat als de toekomstige uitstoot van broeikasgassen wordt beperkt en het akkoord van Parijs wordt nagekomen, er een kans bestaat dat zelfs een bescheiden toename van de neerslag het massaverlies van enkele van de grootste gletsjers van Patagonië kan stoppen. Aan de andere kant, als de uitstoot van broeikasgassen één van de minst optimistische scenario's volgt, is het onwaarschijnlijk dat de neerslag voldoende zal toenemen om verder temperatuur geïnduceerd verlies van Patagonische ijsmassa’s te voorkomen. Om de tweede onderzoeksvraag te beantwoorden, werd de omvang en snelheid van GIA nabij het centrum van de voormalige Patagonische ijskap tijdens het Laat-Glaciaal en Holoceen gereconstrueerd door middel van een multi-proxy analyse van een sedimentkern verzameld in een voorheen marien geïsoleerde baai. Onze resultaten tonen aan dat de glaciale isostatische opvering begon vóór 16,5 cal. kyr BP en dat deze de globale zeespiegelstijging overtrof tot iets voor 9,1 cal. kyr BP. Tussen 16,5 – 9,1 cal. kyr BP steeg de vaste aarde ter hoogte van het centrum van de voormalige Patagonische ijskap ca. 96 m, met een gemiddelde snelheid van 1,3 cm/jaar. De glaciale isostatische opvering ging door (ca. 20 m) gedurende de laatste 9,1 duizend jaar, maar met een langzamer gemiddeld tempo van 0,2 cm/jaar. Onze gegevens suggereren verder dat de GIA snelheid aanzienlijk schommelde binnen deze tijdsintervallen, in reactie op de lokale gletsjerdynamiek. Meer specifiek lijkt het grootste deel van de GIA geregistreerd tussen 16,5 - 9,1 cal. kyr BP te hebben plaatsgevonden vóór smeltwaterpuls 1A (14,5 – 14,0 cal. kyr BP). Gedurende het grootste deel van de laatste 9,1 duizend jaar bleef de GIA relatief langzaam, maar versnelde tijdens het late Holoceen als reactie op veranderingen in Neoglaciale ijsbelasting. Over het algemeen impliceert onze analyse van de GIA nabij het centrum van de voormalige Patagonische ijskap een relatief snelle reactie van de lokale vaste aarde op ijsontlading, wat overeenkomt met onafhankelijke modelleringsstudies die de hedendaagse opwaartse opvering onderzoeken. Wij concluderen dat de vaste aarde ter hoogte van het centrum van de voormalige Patagonische ijskap een glaciale isostatische opvering van ca. 116 m over de laatste 16,5 duizend jaar heeft ervaren, en dat >80% plaatsvond tijdens het Laat-Glaciaal en Vroeg-Holoceen. Over het algemeen hebben onze bevindingen belangrijke implicaties voor de glaciologische toekomst van Patagonië. Ten eerste geven de huidige regionale klimaatprojecties aan dat als we het meest agressieve scenario voor broeikasgasemissies (RCP8.5) blijven volgen, de mogelijke toename in neerslag waarschijnlijk onvoldoende zal zijn om verdere temperatuur geïnduceerde gletsjerafname tegen te gaan. Belangrijk om op te merken is echter de lage betrouwbaarheid van de voorspelde neerslagveranderingen onder het RCP8.5 scenario vanwege de complexe interactie tussen het Andesgebergte en de vochtige westenwinden. Ten tweede zal de snelle glaciale isostatische opvering de komende decennia zeker doorgaan, maar hoe de opveringssnelheden zich in de toekomst zullen ontwikkelen zal sterk afhangen van de neerslag. Bovendien kan deze glaciale isostatische opvering tot op zekere hoogte indirect gletsjers die in zee eindigen stabiliseren, maar dit stabilisatiemechanisme zal waarschijnlijk worden tegengegaan door toekomstige verdunning van deze gletsjers, wat onvermijdelijk lijkt onder RCP8.5. In het algemeen heeft deze thesis aangetoond dat neerslag een belangrijkere rol speelt dan temperatuur in het beheersen van gletsjerfluctuaties op honderdjarige schaal in het westelijke deel van Patagonië, en bij uitbreiding in andere maritieme regio's, en dat de vaste aarde een bijzonder snelle reactie had op veranderingen in ijsbelasting tijdens zowel de laatste deglaciatie als het Neoglaciale tijdperk.

Downloads

  • (...).pdf
    • full text (Published version)
    • |
    • UGent only (changes to open access on 2028-11-13)
    • |
    • PDF
    • |
    • 14.25 MB

Citation

Please use this url to cite or link to this publication:

MLA
Troch, Matthias. Influence of Climate Change on the Postglacial Evolution of Patagonian Glaciers and Response of the Solid Earth. Ghent University. Faculty of Sciences, 2023.
APA
Troch, M. (2023). Influence of climate change on the postglacial evolution of Patagonian glaciers and response of the solid earth. Ghent University. Faculty of Sciences, Ghent, Belgium.
Chicago author-date
Troch, Matthias. 2023. “Influence of Climate Change on the Postglacial Evolution of Patagonian Glaciers and Response of the Solid Earth.” Ghent, Belgium: Ghent University. Faculty of Sciences.
Chicago author-date (all authors)
Troch, Matthias. 2023. “Influence of Climate Change on the Postglacial Evolution of Patagonian Glaciers and Response of the Solid Earth.” Ghent, Belgium: Ghent University. Faculty of Sciences.
Vancouver
1.
Troch M. Influence of climate change on the postglacial evolution of Patagonian glaciers and response of the solid earth. [Ghent, Belgium]: Ghent University. Faculty of Sciences; 2023.
IEEE
[1]
M. Troch, “Influence of climate change on the postglacial evolution of Patagonian glaciers and response of the solid earth,” Ghent University. Faculty of Sciences, Ghent, Belgium, 2023.
@phdthesis{01HF9AEJRED9W6VFW82ED9HQP5,
  abstract     = {{Over the last decades, global warming has caused widespread shrinking of the cryosphere, with two thirds of glaciers worldwide (excluding the Greenland and Antarctic ice sheets) projected to disappear by 2100 CE. Large uncertainties however remain in maritime settings, where some glaciers have recently gained mass in response to increased snowfall or lowered air temperatures related to changes in atmospheric circulation. In addition, worldwide ice-mass loss has caused sea level to rise on a global scale. On a local scale, however, sea level has fallen in glacierized regions due to Glacial Isostatic Adjustment (GIA) of the underlying solid earth related to decreasing ice loads. On these two aspects, Patagonia stands out. Increased precipitation along the western side of the Andean ice divide since the 1980s, for instance, has partly attenuated ice mass loss in response to atmospheric warming. In addition, this region is home to the largest glacial isostatic rebound rate ever recorded, with recent GPS measurements revealing crustal uplift rates exceeding 4 cm/year.

Detailed analyses of past glacier-climate and glacier-isostasy interactions in Patagonia are needed to better assess how future climate change will affect both the local cryo- and lithosphere. Given the location of the Patagonian icefields at the warm end of the continuum of climatic and oceanographic settings at which glaciers reach sea level, conducting research on Patagonian outlet glaciers might also provide us with a crucial window into the future of similar glacierized regions across the world.

With this in mind, the goal of this thesis is to better comprehend how Patagonian outlet glaciers along the maritime side of the southern Andes responded to climate change over the past millennia, and to quantify the magnitude and rate of the associated isostatic response. More specifically, we aim to address two research questions: (1) “What is the relative importance of temperature and precipitation on glacier variability along the humid side of the southern Andes?”, and (2) “How fast and how much did the solid earth respond to post-Last Glacial Maximum ice load changes?”.

To answer the first research question, the postglacial fluctuations of three outlet glaciers located along the hyperhumid western side of the Southern Patagonian Icefield were reconstructed using a multi proxy analysis of a sediment core collected in a proglacial fjord. Our results show that the investigated glaciers retreated into their respective fjords by 11.2 cal kyr BP, and remained relatively stable during the first half of the Holocene. Thereafter, they fluctuated considerably during the Neoglacial period, with four marked episodes of glacier shrinkage at 5.8 – 4.8, 3.9 – 2.4, 1.0 – 0.2 cal kyr BP, and during the 20th century. Furthermore, our analysis of sediment cores collected along the fjord–shelf–slope continuum connecting Patagonia with the Pacific Ocean confirms that fjord sediment cores collected within 40 to 60 km from the present-day ice front, such as the core analyzed in this thesis, are ideally suited to reconstruct glacier fluctuations over the entire Holocene. Although sediment cores located further offshore are necessary to reconstruct pre-Holocene glacier variability, those sites are not sensitive enough to Holocene glacier fluctuations. In addition, the comparison of our sediment record with geological archives from both sides of the Patagonian icefields (46° – 56°S) suggests synchronous glacier variability on multi-centennial timescales during the Neoglacial period, which implies a regional climate control. 

The response of the same three outlet glaciers to changes in air temperature and precipitation during the Neoglacial period was simulated using a numerical ice-flow model. Our experiments show that, on weighted average, precipitation drove 67% of the centennial-scale fluctuations in glacier volume over the last 6000 years. When applied to the temperature projected for the end of this century, our data-validated numerical model indicates that precipitation increases of 10 – 50% are needed to stabilize the investigated glaciers, depending on the climate scenario (SSP1-2.6 to SSP5-8.5). This implies that if future emissions of greenhouse gases are curtailed and the Paris agreement fulfilled, there is a chance that even a modest increase in precipitation can stop mass loss of some of Patagonia’s largest glaciers. On the other hand, if greenhouse-gas emissions follow one of the least optimistic scenarios, it is unlikely that precipitation will increase sufficiently to avoid further temperature-induced ice-mass loss.

To answer the second research question, the magnitude and rate of GIA near the center of the former Patagonian Ice Sheet during the Late Glacial and Holocene was reconstructed through a multi-proxy analysis of a sediment core collected in a previously marine-isolated bay. Our results indicate that glacial isostatic rebound started before 16.5 cal kyr BP and that it outpaced global sea-level rise until slightly before 9.1 cal kyr BP. Between 16.5 – 9.1 cal kyr BP, the center of the former Patagonian Ice Sheet rose ca. 96 m, at an average rate of 1.3 cm/year. Glacial isostatic rebound continued (ca. 20 m) over the last 9.1 kyr, but at a slower average pace of 0.2 cm/year. Our data furthermore suggest that the GIA rate fluctuated considerably within these time intervals, in response to glacier dynamics. More specifically, most of the GIA registered between 16.5 – 9.1 cal kyr BP seems to have occurred before meltwater pulse 1A (14.5 – 14.0 kyr BP). During most of the last 9.1 kyr, GIA remained relatively slow, but accelerated during the late Holocene in response to Neoglacial ice load changes. Overall, our analysis of GIA near the center of the former Patagonian Ice Sheet implies a relatively rapid response of the local solid earth to ice unloading, which is in agreement with independent modelling studies investigating contemporary uplift. We conclude that the center of the former Patagonian Ice Sheet experienced a GIA of ca. 116 m over the last 16.5 kyr, and that >80% occurred during the Late Glacial and early Holocene.

Overall, our findings have important implications for the glaciological future of Patagonia. First, current regional climate projections indicate that if we continue to follow the most aggressive greenhouse gas emission scenario (RCP8.5), the possible increase in precipitation will most likely be insufficient to counter further temperature-induced glacier decline. Important to note, however, is the low confidence of the forecasted precipitation changes under RCP8.5 due to the complex interaction of the Andes with the humid westerly winds, which highlights the urgency to develop local models able to provide accurate and precise forecasts of precipitation change. Second, rapid glacial isostatic rebound will most certainly continue over the coming decades, but how rebound rates will evolve in the future will strongly depend on precipitation. In addition, this glacial isostatic rebound may indirectly stabilize marine-terminating glaciers to some degree, however, this stabilizing mechanism will likely be countered by future glacier thinning, which appears inevitable under RCP8.5. Overall, this thesis has shown that precipitation plays a more important role than temperature in controlling centennial-scale glacier fluctuations in western Patagonia, and by extension in other maritime regions, and that the solid earth had a particularly rapid response to both deglacial and Neoglacial ice-load changes.}},
  author       = {{Troch, Matthias}},
  language     = {{eng}},
  pages        = {{XI, 138}},
  publisher    = {{Ghent University. Faculty of Sciences}},
  school       = {{Ghent University}},
  title        = {{Influence of climate change on the postglacial evolution of Patagonian glaciers and response of the solid earth}},
  year         = {{2023}},
}