ALBERT

Description: Global climate change and the impacts of ocean warming, ocean acidification and declining water quality are adversely affecting coral-reef ecosystems. This is of great concern, as coral reefs provide numerous ecosystem, economic and social services. Corals are also recognised as being amongst the strongest individual sources of natural atmospheric sulfur, through stress-induced emissions of dimethylsulfide (DMS). In the clean marine boundary layer, biogenic sulfates contribute to new aerosol formation and the growth of existing particles, with important implications for the radiative balance over the ocean. Evidence suggests that DMS is not only directly involved in the coral stress response, alleviating oxidative stress, but also may create an “ocean thermostat” which suppresses sea surface temperature through changes to aerosol and cloud properties. This review provides a summary of the current major threats facing coral reefs and describes the role of dimethylated sulfur compounds in coral ecophysiology and the potential influence on climate. The role of coral reefs as a source of climatically important compounds is an emerging topic of research; however the window of opportunity to understand the complex biogeophysical processes involved is closing with ongoing degradation of the world's coral reefs. The greatest uncertainty in our estimates of radiative forcing and climate change is derived from natural aerosol sources, such as marine DMS, which constitute the largest flux of oceanic reduced sulfur to the atmosphere. Given the increasing frequency of coral bleaching events, it is crucial that we gain a better understanding of the role of DMS in local climate of coral reefs.

Description: The mass loss from the Greenland Ice Sheet has increased over the past two decades. Marine-terminating glaciers contribute significantly to this mass loss due to increased melting and ice discharge. Rapid retreat periods of these tidewater glaciers have been linked to the concurrent inflow of warm, Atlantic derived waters. However, little is known about the variability of Atlantic-derived waters within these fjords, due to a lack of multi-annual, in situ measurements. Thus, to better understand the potential role of ocean warming on glacier retreat, reconstructions that characterize the variability of Atlantic water inflow to these fjords are required. Here, we investigate foraminiferal assemblages in a sediment core from Upernavik Fjord, West Greenland, in which the major ice stream Upernavik Isstrøm terminates. We investigate the environmental characteristics that control species diversity and derive that it is predominantly controlled by changes in bottom water variability. Hence, we provide a reconstruction of Atlantic water inflow to Upernavik Fjord, spanning the period 1925–2012. This reconstruction reveals peak Atlantic water inflow during the 1930s and again after 2000, a pattern that is similar to the Atlantic Multidecadal Oscillation (AMO). We compare these results to historical observations of front positions of Upernavik Isstrøm. This reveals that inflow of warm, Atlantic-derived waters indeed likely contributed to high retreat rates in the 1930s and after 2000. However, moderate retreat rates of Upernavik Isstrøm also prevailed in the 1960s/1970s, showing that retreat continued despite reduced Atlantic water inflow, albeit at a lower rate. Considering the link between bottom water variability and the AMO in Upernavik Fjord and the fact that a persistent negative phase of the AMO is expected for the next decade, Atlantic water inflow into the fjord may decrease in the next ~ 10 years.

Description: The mass loss from the Greenland Ice Sheet has increased over the past 2 decades. Marine-terminating glaciers contribute significantly to this mass loss due to increased melting and ice discharge. Periods of rapid retreat of these tidewater glaciers have been linked to the concurrent inflow of warm Atlantic-sourced waters. However, little is known about the variability of these Atlantic-derived waters within the fjords, due to a lack of multi-annual in situ measurements. Thus, to better understand the potential role of ocean warming on glacier retreat, reconstructions that characterize the variability of Atlantic water inflow to the fjords are required. Here, we investigate foraminiferal assemblages in a sediment core from Upernavik Fjord, West Greenland, in which the major ice stream Upernavik Isstrøm terminates. We conclude that the foraminiferal assemblage is predominantly controlled by changes in bottom water composition and provide a reconstruction of Atlantic water inflow to Upernavik Fjord, spanning the period 1925–2012. This reconstruction reveals peak Atlantic water influx during the 1930s and again after 2000, a pattern that is comparable to the Atlantic Multidecadal Oscillation (AMO). The comparison of these results to historical observations of front positions of Upernavik Isstrøm reveals that inflow of warm Atlantic-derived waters likely contributed to high retreat rates in the 1930s and after 2000. However, moderate retreat rates of Upernavik Isstrøm also prevailed in the 1960s and 1970s, showing that glacier retreat continued despite a reduced Atlantic water inflow, albeit at a lower rate. Considering the link between bottom water variability and the AMO in Upernavik Fjord, and the fact that a persistent negative phase of the AMO is expected for the next decade, Atlantic water inflow into the fjord may decrease in the coming decade, potentially minimizing or stabilizing the retreat of Upernavik Isstrøm during this time interval.