Seasonal changes of Antarctic marine bacterioplankton

During a one-year period the development of the Antarctic coastal seawater bacterioplankton was followed. Two field stations (surface and deep water = 20 m, respectively) were sampled daily in 1989 in " Terre Adelie area". The survey included physicochemical (temperature and particulate organic matter) and bacteriological (total and heterotrophic bacteria, bacterial production) measurements. Whereas bacterial parameters at the deep water station remained fairly constant, bacterial parameters in surface waters generally increased during the year obviously related to the formation of sea ice

CO2 and CH4 in sea ice from a subarctic fjord under influence of riverine input

We present the CH4 concentration [CH4], the partial pressure of CO2 (pCO2) and the total gas content in bulk sea ice from subarctic, land-fast sea ice in the Kapisillit fjord, Greenland. Fjord systems are characterized by freshwater runoff and riverine input and based on dδ18O data, we show that > 30% of the surface water originated from periodic river input during ice growth. This resulted in fresher sea-ice layers with higher gas content than is typical from marine sea ice. The bulk ice [CH4] ranged from 1.8 to 12.1 nmol Lg-1, which corresponds to a partial pressure ranging from 3 to 28 ppmv. This is markedly higher than the average atmospheric methane content of 1.9 ppmv. Evidently most of the trapped methane within the ice was contained inside bubbles, and only a minor portion was dissolved in the brines. The bulk ice pCO2 ranged from 60 to 330 ppmv indicating that sea ice at temperatures above -4 °C is undersaturated compared to the atmosphere (390 ppmv). This study adds to the few existing studies of CH4 and CO2 in sea ice, and we conclude that subarctic seawater can be a sink for atmospheric CO2, while being a net source of CH4

Melt pond biogeochemistry in central Arctic: first insights from MOSAiC campaign

We undertook a melt pond survey during the international drift campaign MOSAiC Leg 5 (from 22 August to 18 September 2020) to understand variations in climate gases (CO2, CH4, N2O and DMS) and nutrients in melt ponds during the open water and freezing periods, and to study the interactions with atmospheric and ecological parameters (Figure 1a). Inside those melt ponds with a darker color, we found significant quantities of floating organic material within the pond water, along with significant further organic material settled at the bottom of the pond and frozen into the ice (Figure 1b). These floating and sedimented materials were both white and green/brown; the green/brown material was mainly composed of phytoplankton “Melosira arctica”, while the white material was composed of re-mineralized organic matter during degradation (including the remains of krill and other zooplankton). There were strong vertical gradients in physical parameters from the surface to the bottom of the melt pond (within 1 m depth): from +0.2°C to –1.5°C for temperature, from 0 to 29 psu for salinity, and 9.2 to 13.5 mg L–1 for dissolved oxygen (DO). The DO minimum layer (below 9 mg L–1) corresponded with a salinity of 25 psu, which generally occurred at approximately 0.6 m depth, and it increased to over 13 mg L–1 at the atmospheric interface. At the end of Leg 5 (mid-September 2020), these strong gradients disappeared, likely due to the mixing events during the cooling and freezing periods. Prior to and during the freezing period, CO2 flux was measured periodically within the melt pond with a floating chamber system. Because measured in situ CO2 concentration at the melt pond surface (top 10 cm) was low (321 ppm) compared to the atmosphere (approximately 400 ppm), air–to-melt pond CO2 flux was negative (melt pond was acting as a sink for atmospheric CO2) around –3.9 mmol m–2 day–1. Therefore, the melt pond water absorbs significant amounts of CO2 from the atmosphere. We also found extremely low CO2 concentrations (170 ppm) at the freshwater/seawater interface (0.6 m depth) corresponding to the same depth as the DO minimum. Therefore, we expected that if melt pond water is mixed vertically by the wind, cooling, crack formation, and ice movement, the melt pond could become an even stronger sink for atmospheric CO2. Ice cores collected from the bottom of the melt pond were porous at the top 0.50 m, and contain large quantities of organic material similar to that identified floating in the water column This accumulation of material and ongoing degradation processes over the pond bottom ice would contribute significantly to the turnover of carbon, sulphur and nitrogen containing gases cycles within melt pond water and thereby gas exchange process with the atmosphere.MOSAi

Determination of air‐sea ice transfer coefficient for CO2: Significant contribution of gas bubble transport during sea ice growth

Air‐ice CO2 fluxes were measured continuously from the freezing of a young sea‐ice cover until its decay. Cooling seawater was as a sink for atmospheric CO2 but asthe ice crystalsformed,sea ice shifted to a source releasing CO2 to the atmosphere throughout the whole ice growth. Atmospheric warming initiated the decay, re‐shifting sea‐ice to a CO2 sink. Combining these CO2 fluxes with the partial pressure of CO2 within sea ice, we determined gas transfer coefficients for CO2 at air‐ice interface for growth and decay. We hypothesize that this difference originates from the transport of gas bubbles during ice growth, while only diffusion occurs during ice melt. In parallel, we used a 1D biogeochemical model to mimic the observed CO2 fluxes. The formation of gas bubbles was crucial to reproduce fluxes during ice growth where gas bubbles may account for up to 92 % of the upward CO2 fluxes

Non-Gaussian power grid frequency fluctuations characterized by Levy-stable laws and superstatistics

Multiple types of fluctuations impact the collective dynamics of power grids and thus challenge their robust operation. Fluctuations result from processes as different as dynamically changing demands, energy trading and an increasing share of renewable power feed-in. Here we analyse principles underlying the dynamics and statistics of power grid frequency fluctuations. Considering frequency time series for a range of power grids, including grids in North America, Japan and Europe, we find a strong deviation from Gaussianity best described as Lévy-stable and q-Gaussian distributions. We present a coarse framework to analytically characterize the impact of arbitrary noise distributions, as well as a superstatistical approach that systematically interprets heavy tails and skewed distributions. We identify energy trading as a substantial contribution to today’s frequency fluctuations and effective damping of the grid as a controlling factor enabling reduction of fluctuation risks, with enhanced effects for small power grids

The Weddell Gyre, Southern Ocean: present knowledge and future challenges

The Weddell Gyre (WG) is one of the main oceanographic features of the Southern Ocean south of the Antarctic Circumpolar Current which plays an influential role in global ocean circulation as well as gas exchange with the atmosphere. We review the state‐of‐the art knowledge concerning the WG from an interdisciplinary perspective, uncovering critical aspects needed to understand this system's role in shaping the future evolution of oceanic heat and carbon uptake over the next decades. The main limitations in our knowledge are related to the conditions in this extreme and remote environment, where the polar night, very low air temperatures and presence of sea ice year‐round hamper field and remotely sensed measurements. We highlight the importance of winter and under‐ice conditions in the southern WG, the role that new technology will play to overcome present‐day sampling limitations, the importance of the WG connectivity to the low‐latitude oceans and atmosphere, and the expected intensification of the WG circulation as the westerly winds intensify. Greater international cooperation is needed to define key sampling locations that can be visited by any research vessel in the region. Existing transects sampled since the 1980s along the Prime Meridian and along an East‐West section at ~62°S should be maintained with regularity to provide answers to the relevant questions. This approach will provide long‐term data to determine trends and will improve representation of processes for regional, Antarctic‐wide and global modeling efforts – thereby enhancing predictions of the WG in global ocean circulation and climate

Rapid decline of the CO2 buffering capacity in the North Sea and implications for the North Atlantic Ocean

Author Posting. © American Geophysical Union, 2007. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Global Biogeochemical Cycles 21 (2007): GB4001, doi:10.1029/2006GB002825.New observations from the North Sea, a NW European shelf sea, show that between 2001 and 2005 the CO2 partial pressure (pCO2) in surface waters rose by 22 μatm, thus faster than atmospheric pCO2, which in the same period rose approximately 11 μatm. The surprisingly rapid decline in air-sea partial pressure difference (ΔpCO2) is primarily a response to an elevated water column inventory of dissolved inorganic carbon (DIC), which, in turn, reflects mostly anthropogenic CO2 input rather than natural interannual variability. The resulting decline in the buffering capacity of the inorganic carbonate system (increasing Revelle factor) sets up a theoretically predicted feedback loop whereby the invasion of anthropogenic CO2 reduces the ocean's ability to uptake additional CO2. Model simulations for the North Atlantic Ocean and thermodynamic principles reveal that this feedback should be stronger, at present, in colder midlatitude and subpolar waters because of the lower present-day buffer capacity and elevated DIC levels driven either by northward advected surface water and/or excess local air-sea CO2 uptake. This buffer capacity feedback mechanism helps to explain at least part of the observed trend of decreasing air-sea ΔpCO2 over time as reported in several other recent North Atlantic studies.S. Doney and I. Lima were supported by NSF/ONR NOPP (N000140210370) and NASA (NNG05GG30G)

The making of a mammalian peroxisome, version 2.0: mitochondria get into the mix

This is the author accepted manuscript. The final version is available from Nature Publishing Group via the DOI in this record.A recent report from the laboratory of Heidi McBride (McGill University) presents a role for mitochondria in the de novo biogenesis of peroxisomes in mammalian cells (1). Peroxisomes are essential organelles responsible for a wide variety of biochemical functions, from the generation of bile, to plasmalogen synthesis, reduction of peroxides, and the oxidation of very long chain fatty acids (2). Like mitochondria, peroxisomes proliferate primarily through growth and division of pre-existing peroxisomes (3-6). However, unlike mitochondria, peroxisomes do not fuse (5,7); further, and perhaps most importantly, they can also be born de novo, a process thought to occur through the generation of pre-peroxisomal vesicles that originate from the endoplasmic reticulum (reviewed in (8,9). De novo peroxisome biogenesis has been extensively studies in yeast, with a major focus on the role of the ER in this process. Comprehensive studies in mammalian cells are, however, scarce (5,10-12). By exploiting patient cells lacking mature peroxisomes, Sugiura et al. (1) now assign a role to ER and mitochondria in de novo mammalian peroxisome biogenesis by showing that the formation of immature preperoxisomes occurs through the fusion of Pex3- / Pex14-containing mitochondriaderived vesicles with Pex16-containing ER-derived vesicles