Øyvind Paasche

Reconstructing Climate Change: Not All Glaciers Suitable

Glaciers are among the most trusted indicators of climate change, not just because they retreat due to the current rise in global temperatures but also because of their central role in reconstructing past climates. Glaciers come in many forms, and their sensitivity to climate change depends partly on the physics governing the individual glacier, implying that a response can be fast or slow, straightforward or complex, which in sum suggests that not all glaciers are equally suitable for reconstructing past and present climate conditions. In particular, surging and debris-covered glaciers may especially yield misleading results (Figure 1).

Synchronized postglacial colonization by magnetotactic bacteria

The primary succession history of magnetotactic bacteria (MTB) is reconstructed in postglacial lake sediments using a rock magnetic approach that discriminates biologically produced magnetite from nonorganic magnetic carriers. MTB are among the oldest prokaryotes found in the fossil record, but little is known about how they have colonized and recolonized habitats around the world. Here we observe how MTB synchronously colonized 4 freshwater lakes 9760 ± 160 yr ago. The lakes are more than 1400 km apart, representing both coastal and inland regions, and have altitudinal differences of almost 800 m. The synchronous colonization of Norway (and possibly Sweden) suggests that the pathways were extremely efficient, and that the sources must have been wide ranging. We propose that birds could have carried and spread the bacteria as northward migration routes were reestablished following the onset of the current interglacial. This unique data set underscores the tenacity of MTB as evolutionary survivors, and also demonstrates their response to large-scale environmental changes in ways not previously anticipated.

Effects of hydrogen peroxide treatment on measurements of lake sediment grain-size distribution

Grain-size analysis is routinely performed on soft sediments, and has been applied in numerous paleoenvironmental studies using lake sediment archives. Despite the frequent use of this method, no common protocol exists for the treatment of lake sediment samples prior to analysis. In this study, differences in grain-size distribution before and after treatment with hydrogen peroxide (H2O2) were evaluated for sediment sequences from four lakes in Norway characterized by different geological and environmental settings. We found that removal of organic matter had a profound effect on the grain-size distribution of the sediment samples, which might have important bearing on how such data are interpreted. One of the analysed sediment sequences showed a systematic shift toward more fines after treatment, whereas no clear systematic effects were observed for the remaining three. The observed differences might derive from (1) variable concentrations of biogenic silica, which could cause shifts in the Sedigraph readings as a consequence of the porosity and fragility of diatom frustules, (2) clogging of organic matter during initial mechanical sieving, and (3) disturbance of the internal flow regime in the Sedigraph as a result of the dispersive agent having a viscosity that is too low. These possible explanations require further testing. Nevertheless, we propose that the paleolimnological community should develop a common protocol for pre-treatment of sediments from lacustrine settings that both enables reproducibility of results and reduces the risk of misinterpretation. Our observations suggest that sediments from boreal lakes should be treated with hydrogen peroxide prior to grain-size analysis, although treatment should be relatively mild to avoid possible mineral degradation.

The New Arctic

In the late eighteenth century explorers and scientists started venturing into the Arctic beyond areas that were already populated by Indigenous peoples and a smaller number of new settlers, and ultimately towards the North Pole. It was about as far as anyone could get from civilization at the time, and in many respects it remains this way to this day. What the fi rst explorers saw had not yet been seen and recorded by Western civilization. They were the fi rst to tell the stories and document the state of the Arctic – its physical landscape and Indigenous cultures. The prosaic descriptions are many and colourful, moving and poetic, and they also soon began to provide detailed accounts of the state of Indigenous living conditions. A shared feature in these fi rst accounts, in prints and in paintings, is the descriptions of a harsh and barren landscape frozen in time; static and unchangeable, except for the swift sways in weather. Fanciful images of indigenous communities in isolated settlements, without any contact with “western civilization” came to shape the following generations perception of the Arctic. While the Arctic gradually became a place where new maps and lines drawn became a reality to outsiders, it was also, and had been for thousands of years, the homeland for many and diverse groups of indigenous peoples, surviving in at times unforgiving conditions while developing vibrant cultures, including strong traditions for adapting to changing conditions. The storytelling is today highly valued by itself and for its importance as a complement to science. And northern art has become more vibrant than ever as shown in some chapters here integrating the changes occurring on so many grounds. B. Evengård , MD, PhD (*) Division of Infectious Diseases, Department of Clinical Microbiology , Umeå University Hospital , Umeå SE-901 85 , Sweden e-mail: birgitta.evengard@umu.se Ø. Paasche , PhD Bergen Marine Research Cluster , Professor Keysersgt. 8 , Bergen NO-5020 , Norway University of the Arctic (UArctic) , PO Box 122 , Rovaniemi FI-96101 , Finland e-mail: Oyvind.paasche@uib.no J. N. Larsen Stefansson Arctic Institute and University of Akureyri , Akureyri , Iceland e-mail: jnl@unak.is

How Does Climate Impact Floods? Closing the Knowledge Gap

Destructive floods impose severe consequences on societies, leaving havoc and death in their wake. Annually, an average of 9000 people are killed, and 115 million require immediate assistance or are displaced by floods worldwide. Because of population increase in flood-prone areas alone, the number of people exposed to floods in North America is expected to almost double in 2030 compared to 1970 [National Research Council, 2013]. It is no wonder that floods are considered serious threats by government agencies and municipal planners, but the impact of climate change on these numbers is still somewhat uncertain.

Magnetic and geochemical signatures of flood layers in a lake system

River floods holds the capasity to erode and transport sediments that are deposited whenever the discharge is redused. In catchments that are subjected to repeated flooding, downstream lakes can therefore contain a record of past events across multiple timescales. High-resolution core scanning analyses such as X-ray fluorescence (XRF) scanning and magnetic susceptibility (MS) provide data that are frequently used to detect flood layers in soft sediment archives such as lakes, fjords and ocean basins. Deposits of past floods also can potentially reveal information about the evolution of flood events as well as source area. Here we explore ways in which subtle variability in high-resolution data can be utilized and subsequently vetted by high-precision measurements in order to delineate the copious information that can be extracted from soft sediment records. By combining magnetic hysteresis measurements and first-order reversal curves (FORCs) with inductively coupled plasma optical emission spectrometer (ICP-OES) measurements of chemical elements on 36 samples, questions about flood dynamics and variability are raised, and also sources of noise in high-resolution scanning techniques are discussed. Specifically, we show that a lake flood record from Southern Norway containing 92 floods distributed over 10,000 years can be sub-divided into two groups of floods that were generated either by spring snow melting, intense summer rainstorms, or a combination of both. The temporal evolution of this pattern shows a marked shift towards spring floods around 2000 years ago compared to the earlier part of the record. This article is protected by copyright. All rights reserved.

Cirque Glacier on South Georgia Shows Centennial Variability over the Last 7000 Years

A 7000 year-long cirque glacier reconstruction from South Georgia, based on detailed analysis of fine-grained sediments deposited downstream in a bog and a lake, suggests continued presence during most of the Holocene. Glacier activity is inferred from various sedimentary properties including magnetic susceptibility (MS), dry bulk density (DBD), loss-on-ignition (LOI) and geochemical elements (XRF), and tallied to a set of terminal moraines. The two independently dated sediment records document concurring events of enhanced glacigenic sediment influx to the bog and lake, whereas the upstream moraines afford the opportunity to calculate past Equilibrium Line Altitudes (ELA) which has varied in the order of 70 m altitude. Combined, the records provide new evidence of cirque glacier fluctuations on South Georgia. Based on the onset of peat formation, the study site was deglaciated prior to 9900±250 years ago when Neumayer tidewater glacier retreated up-fjord. Changes in the lake and bog sediment properties indicate that the cirque glacier was close to its maximum Holocene extent between 7200±400 and 4800±200 cal BP, 2700±150 and 2000±200 cal BP, 500±150-300±100 cal BP, and in the 20th century (likely 1930s). The glacier fluctuations are largely in-phase with reconstructed Patagonian glaciers, implying that they respond to centennial climate variability possibly connected to corresponding modulations of the Southern Westerly Winds.

The wicked ocean

Anthropogenically induced climate change has created a set of intriguing scientific problems pertaining to the Seas and the Oceans on earth that can be monitored, analysed, modelled and consequently understood at some level. The international research community is deeply engaged in this endeavour as exemplified by the United Nations Decade of Ocean Science for Sustainable Development (2021–2030). Even so, the types of problems caused by human activity are inherently difficult to solve, if solvable at all, making them equally difficult to approach and manage. Here we address these as ‘wicked problems’ (first discussed by Churchman 1967, and later defined and formalized regarding social and natural sciences by Rittel and Webber 1973), posing challenges that currently seem to surpass our ability to tackle them. We see the Sea and the Oceans, but mainly from above—we see only the surface. A curved and broken line that separates our world from the one below, from the life in and of the Sea. Seen from ashore, its beauty and incessant perplexity is staggering—an outlook which we increasingly seek refuge in, for recreation and for wellbeing (see for instance Bowen et al. 2014). Our land-based perspective is rewarding, but also limiting in its lack of three-dimensionality, because the vastness of the Seas and the Oceans is so much more than the surface we observe from a distance. It is what we cannot see which makes it so challenging to understand. Water stretches across basins and beneath ice shelves, extending all the way down to the abyssal depths. The Seas and Oceans cover over 70% of Earth’s surface or 3.61 9 10 km with a total mass of 1.4 9 10 kg (Vallis 2011). It has a mean depth of over 3.7 km, but even so all water on Earth can still be fitted in a sphere of only 1400 km in diameter. Despite big numbers, clean water is a scarce commodity that needs to be treated accordingly. Ocean circulation and overturning, processes that involve wind-driven gyres, turbulent diffusion and the sinking of surface water, are unevenly distributed globally. Gebbie and Huybers (2011) estimate that 15% of the total ocean’s surface accounts for 85% of the production of deep water. Despite the fact that this production is localized to a few high latitude areas, it still enables continued water mass exchange between the major interhemispheric basins. This vital engine helps maintain a balance in earth’s climate by constantly moderating it through uptake of heat and subsequent redistribution. On a human time scale, the ocean engine is slow, given the volume in question, explainingwhy it can take up to 1200–1500 years before submerged surface water in the PacificOcean reach the deepest parts of the basin (Gebbie and Huybers 2012) or even longer before it resurfaces, all depending on which ocean and water mass you examine (Wunsch and Heimbach 2008). It is that sluggishness we have come to rest the fundaments of our fast-growing and fast-living civilizations on because if the heat absorbed was released back from the ocean on shorter time scales the impact of our expanding footprint would be immediately evident. This is but one explanation for why we have taken the goods and services provided by the Seas and Oceans for granted through the centuries, a type of behaviour which has cemented a view that is hard to change. Numerous species have been decimated until saved in the last hour like the Antarctic blue whale (Attard et al. 2016) or the sea otter (Doroff et al. 2003). The list of threatened species is growing by the day which in effect makes the global marine ecosystem less resilient to further change (Levin and Lubchenco 2008).

Paths to the New Arctic

In the late eighteenth century explorers and scientists started venturing into the Arctic beyond areas that were already populated by Indigenous peoples and a smaller number of new settlers, and ultimately towards the North Pole. It was about as far as anyone could get from civilization at the time, and in many respects it remains this way to this day.

The Fleeting Glaciers of the Arctic

Glaciers and snow are the very symbol of the Arctic, covering large parts of its terrestrial surface throughout the year. The cool temperatures that have allowed for the widespread coverage of glaciers are now trending towards a warmer climate, and with this gradual shift we observe an abrupt response in the cryosphere of which glaciers are a key component. This change is manifested in retreating fronts and an overall thinning. Because the typology of Arctic glaciers is rich and varied, the response pattern to the on-going warming is not unison. Instead, there are large spatial variations due to the critical balance between summer temperature and winter precipitation in addition to other factors such as aspect, altitude, geographical location, debris cover, calving and so forth. Still, minor variations is superimposed on a larger trends which suggests that in a not so distant future, glaciers will probably be less abundant than what has been common for the last 100 years. In the context of the last 10,000 years it is evident that arctic glaciers have changed significantly and they have even been smaller than they are today, which was the case 9,000 to 5,000 years ago. On Svalbard, two glacier lake sediment records foretell of large past variations, indicating a more articulated sensitivity to climate change than what is commonly perceived for the Arctic cryosphere.