Faculty Talks

March 9^th, 2011


Arctic Geomicrobiology: A Constant Flux of Thermophilic Bacteria into Permanently Cold Marine Sediments.
                                                                                                                                          .pdf
Abstract:

Geomicrobiological investigations of Svalbard fjord sediments over the past 20 years have led to several new insights into cold-adapted Arctic microbial communities and biogeochemical cycling in permanently cold habitats. Temperature adaptation studies have revealed, surprisingly, that in addition to psychrophilic microbial communities, Arctic marine sediments (80° North) also contain large numbers of thermophilic bacteria — up to 105 dormant cells per gram of sediment. Identifying and quantifying misplaced organisms like Arctic thermophiles can highlight mechanisms of cell dispersal that shape microbial diversity and biogeography, and that maintain natural microbial ‘seed banks’. Results from sediment age modelling and endospore germination experiments reveal a stable supply of thermophilic bacteria into the cold Arctic seabed at an annual rate exceeding 108 spores per square metre. These metabolically and phylogenetically diverse Firmicutes show no detectable activity at cold in situ temperatures (~0°C year round), but are induced to rapidly mineralise organic matter by anaerobic hydrolysis, fermentation, and sulfate reduction in sediment incubated at 50°C. The closest known relatives to these bacteria come from warm subsurface petroleum reservoir and ocean crust ecosystems, suggesting that seabed fluid flow from the geosphere is constantly delivering thermophiles from deep biospheres to the cold ocean. Transport pathways linking the geosphere, hydrosphere and biosphere may broadly influence microbial community composition in the marine environment, and might lead to biogeography-based prospecting for geofluid seepage from sub-marine hot spots including not-yet-discovered petroleum reservoirs.

 

---

March 10^th, 2011


Nitrogen dynamics of the Bering shelf inferred from nitrate N and O isotopes: Benthic processes in a changing climate.
                                                                                                                                          .pdf
Abstract:

The expansive continental shelf of the Bering Sea is characterized by a prolific ecosystem that is host to large populations of marine mammals and seabirds as well as to the largest U.S. fishery. The productivity of the shelf is due primarily to the high concentrations of unconsumed nutrients that shoal onto the shallow continental shelf, fueling strong seasonal blooms upon sea ice retreat. I present results from a study of N dynamics of the shelf as part of the Bering Ecosystem Study (BEST) in early spring of 2007 and 2008, which uncovered important insights on the sources and fate of fixed N on the eastern Bering Sea shelf. Measurements of the natural abundance isotopic composition of NO₃ - (¹⁵N/¹⁴N and ¹⁸O/¹⁶O, expressed d¹⁵N (‰ vs. air) and d ¹⁸O (‰ vs. SMOW), respectively) and other N species in shelf waters provided an integrative constraints on the origins of the wintertime NO₃ - that fuels the nascent spring blooms. The data revealed that benthic processes influence the speciation and the burden of fixed N in the wintertime water column considerably. In particular, sediment recycling remobilizes fixed N to the ice-covered water column, contributing substantially to the seasonal replenishment of NO₃ - in shelf waters. The NO₃ - isotope ratios also identified coupled nitrification-denitrification in sediments as the likely mechanism of fixed N loss on the shelf. These processes uncovered here are assessed in the context of the changing shelf hydrography and sea ice extent due to climate warming.

 

---

March 11^th, 2011


Variability and change in the Arctic Ocean
                                                                                                                                          .pdf
Abstract:

The Arctic Ocean has been undergoing large changes in the last decades, ranging from reductions in the sea- ice extent, ice thickness, and ice age to changes in the storage of freshwater, a shift in the pathways of river runoff in the ocean, and a warming of the surface ocean. Due to the short timeseries of many important variables in the Arctic, the mechanisms behind many of these changes are not yet clear. As changes in the Arctic can affect the climate worldwide by reducing the deep-water formation in the North Atlantic and increasing the absorption of solar radiation, a better understanding of the variability in the Arctic climate system is not just crucial for adaptation in the Arctic, but also for improved global climate projections.

In my talk I will highlight what is driving the variability of the freshwater export from the Arctic Ocean over time, how this export might change in a warmer climate with a seasonally ice-free Arctic Ocean, and how it could affect the deep-water convection in the North Atlantic. Furthermore, I will show how the Arctic sea-ice is predicted to change over the 21^st century, and how large the contribution of natural variability is to the observed and predicted sea-ice decline.

 

---

March 14^th, 2011


Primary producers in an ice-covered marine environment.
                                                                                                                                          .pdf
Abstract:

The Arctic ice-covered marine environment is undergoing unprecedented changes in response to our warming climate, with a recent accelerated decline in sea ice cover and changes to water mass characteristics and distribution. It has been hypothesized that the timing and location of primary production will dictate the extent of ice-pelagic-benthic coupling in the ice-covered ecosystem, providing a sensitive indicator for the system's response to the changing environment. Therefore, an encompassing objective of my research has been to examine physical and biological processes controlling the timing, magnitude and location of primary production in the ice-covered marine ecosystem. In particular, I have investigated algae that grow within the sea ice, the ice meltwater, and within the underlying water column. In my talk, I will discuss biophysical processes that affect the growth and decline of these three algal communities in the Canadian high Arctic. I also propose a set of research projects that will further advance knowledge in the field of polar marine science.

 

---

March 15^th, 2011


Recent and long-term changes in the Arctic climate system
                                                                                                                                          .pdf
Abstract:

Over the past several decades, the Arctic regions have undergone substantial change. A high-latitude warming rate over 1875–2008 was 1.36°C/century, almost two times stronger than the Northern Hemisphere trend, with the accelerated warming rate in the recent decade (1.35°C/decade). Oceanographic data demonstrated that over the 20th century the central Arctic Ocean became increasingly saltier and warmer. This warming of the Arctic Ocean culminated in 2007 when the water temperature anomalies were up to 1oC and higher relative to climatology. Concurrent reductions have been documented in arctic ice extent and its thickness culminating in recent dramatic loss of arctic ice. However, high-latitude warming has been uneven in time and was modulated by strong variability. A large- amplitude multidecadal-scale mode with an approximate time scale of 50–80 years was prevalent. We estimate that this mode accounts for ~50% of Arctic atmospheric warming since 1979. Elucidating the mechanisms driving multidecadal variability will be critical to our understanding of the complex nature of changes detected in the Arctic climate system.

 

---

March 16^th, 2011


Elemental Biogeochemical Cycling along Arctic Continental Margins
                                                                                                                                          .pdf
Abstract:

Arctic continental margins are important sites for the cycling of organic carbon and associated elements (nutrients, trace elements, contaminants). Ongoing and projected future changes in Arctic temperatures, river inflow, relative sea level, and sea ice conditions and enhanced development activities along Arctic coasts will affect this cycling, with consequences for local ecosystems and global cycles. However, the variability of environmental conditions along Arctic margins means that predicting the effects of change requires in-depth understanding of organic carbon sources and the sedimentary and oceanographic processes controlling regional and local carbon production, transport and burial. In this presentation, I will discuss recent research findings from Hudson Bay and the Arctic margin spanning northern North America, in which the application of various tracers (δ¹³C, δ¹⁵N, lignin, redox elements, radioisotopes, δ¹⁸O) in sediments and the water column have provided insights into elemental biogeochemical cycling in different systems, and the way these cycles might be expected to change. I will also discuss future research interests, with potential opportunities for student engagement.

 

---

March 18^th, 2011


Light absorption in a melting Arctic sea-ice environment
                                                                                                                                          .pdf
Abstract:

The absorption of solar radiation with sea ice and the upper ocean is responsible for most of the sea ice melting occurring in the Arctic. Ice melting and solar heating stabilizes the upper ocean, and impacts on the air-sea exchange of gas and heat. Furthermore, solar radiation is a requirement for primary production whose annual maximum coincides with the peak in solar radiation levels and ice melting. Yet, how light interacts with the highly variegated melting sea ice cover is not known well enough to allow predictions of impacts caused by a changing Arctic climate. In this presentation, I will discuss how the optical properties of the upper layers of the ocean affect light absorption by presenting some new results from the recent MALINA cruise. Then I will talk about how the absorption of solar radiant energy is partitioned within the sea ice cover and the upper ocean. It is clear that to understand light propagation in natural sea ice and seawater, it is necessary to consider the physics, biology and chemistry that control the interaction of light with these environments. I will conclude by discussing some ideas on how the small-scale sea ice structure thereby may influence biological production within sea ice.