ALBERT

Description: A comprehensive set of autonomous, ice-ocean measurements were collected across the Canada Basin to study the summer evolution of the ice-ocean boundary layer (IOBL) and ocean mixed layer (OML). Evaluation of local heat and freshwater balances and associated turbulent forcing reveals that melt ponds (MP's) strongly influence the summer IOBL-OML evolution. Areal expansion of MP's in mid-June start the upper ocean evolution resulting in significant increases to ocean absorbed radiative flux (19 Wm −2 in this study). Buoyancy provided by MP drainage shoals and freshens the IOBL resulting in a 39 MJm −2 increase in heat storage in just 19 days (52% of the summer total). Following MP drainage, a near-surface fresh layer deepens through shear-forced mixing to form the summer mixed layer (sML). In late summer, basal melt increases due to stronger turbulent mixing in the thin sML and the expansion of open water areas due in part to wind forced divergence of the sea ice. Thermal heterogeneities in the marginal ice zone (MIZ) upper ocean led to large ocean-to-ice heat fluxes (100-200 Wm −2 ) and enhanced basal ice melt (3-6 cm-day −1 ), well away from the ice edge. Calculation of the upper ocean heat budget show that local radiative heat input accounted for at least 89% of the observed latent heat losses and heat storage (partitioned 0.77/0.23). These results suggest that the extensive area of deteriorating sea ice observed away from the ice edge during the 2014 season, termed the “thermodynamically forced MIZ,” was driven primarily by local radiative forcing. This article is protected by copyright. All rights reserved.

Description: The high prevalence of dioecy in marine angiosperms or seagrasses (〉50% of all species) is thought to enforce cross-fertilization. However, seagrasses are clonal plants, and they may still be subject to sibling-mating or bi-parental inbreeding if the genetic neighborhood is smaller than the size of the genets. We tested this by determining the genetic neighborhoods of the dioecious seagrass Thalassia testudinum at two sites (Back-Reef and Mid-Lagoon) in Puerto Morelos Reef Lagoon, Mexico, by measuring dispersal of pollen and seeds in situ, and by fine-scale spatial autocorrelation analysis with eight polymorphic microsatellite DNA markers. Prevalence of inbreeding was verified by estimating pairwise kinship coefficients; and by analysing the genotypes of seedlings grown from seeds in mesocosms. Average dispersal of pollen was 0.3–1.6 m (max. 4.8 m) and of seeds was 0.3–0.4 m (max. 1.8 m), resulting in a neighborhood area of 7.4 m 2 (range 3.4–11.4 m 2 ) at Back-Reef and 1.9 (range 1.87–1.92 m 2 ) at Mid-Lagoon. Neighborhood area (Na) derived from spatial autocorrelation was 0.1–20.5 m 2 at Back-Reef and 0.1–16.9 m 2 at Mid-Lagoon. Maximal extensions of the genets, in 19 × 30 m plots, were 19.2 m (median 7.5 m) and 10.8 m (median 4.8 m) at Back-Reef and Mid-Lagoon. There was no indication of deficit or excess of heterozygotes nor were coefficients of inbreeding ( F IS ) significant. The seedlings did not show statistically significant deficit of heterozygotes (except for 1 locus at Back-Reef). Contrary to our expectations, we did not find evidence of bi-parental inbreeding in this dioecious seagrass with large genets but small genetic neighborhoods. Proposed mechanisms to avoid bi-parental inbreeding are possible selection against homozygotes during fecundation or ovule development. Additionally, the genets grew highly dispersed (aggregation index Ac was 0.09 and 0.10 for Back-Reef and Mid-Lagoon, respectively); such highly dispersed guerrilla-like clonal growth form likely increases the probability of crossing between different potentially unrelated genets. We expected bi-parental inbreeding in Thalassia testudinum , a dioecious seagrass with large genets but very limited pollen and seed dispersal; thus, small genetic neighbourhoods. However, kinship and seedling analysis did not find any evidence for this, which may be attributed to a highly dispersed guerrilla-like clonal growth form (which is unusual for a clonal climax species) that increases the probability of crossing between different potentially unrelated genets.

Description: Paleoclimate data assimilation has recently emerged as a promising technique to estimate past climate states. Here we test two of the underlying assumptions of paleoclimate data assimilation as applied so far: (1) climate proxies can be modeled as linear, univariate recorders of temperature; and (2) structural errors in GCMs can be neglected. To investigate these two points and related uncertainties, we perform a series of synthetic, paleoclimate data assimilation-based reconstructions where ‘pseudo’ proxies are generated with physically-based proxy system models (PSMs) for coral δ 18 O , tree-ring width, and ice core δ 18 O using two isotope-enabled atmospheric general circulation models. For (1), we find that linear univariate models efficiently capture the GCM's climate in ice cores and corals, and do not lead to large losses in reconstruction skill. However, this does not hold for tree-ring width, especially in regions where it is dominated by moisture supply; we quantify how the breakdown of this assumption lowers reconstruction skill for each proxy class. For (2), we find that climate model biases can introduce errors that greatly reduce reconstruction skill, with or without perfect proxy system models. We explore possible strategies for mitigating structural modeling errors in GCMs, and discuss implications for paleoclimate reanalyses. This article is protected by copyright. All rights reserved.

Description: The eddy field across the Arctic Ocean's Canada Basin is analyzed using Ice-Tethered Profiler (ITP) and moored measurements of temperature, salinity and velocity spanning 2005 to 2015. ITPs encountered 243 eddies, 98% of which were anticylones, with approximately 70% of these having anomalously cold cores. The spatially and temporally varying eddy field is analyzed accounting for sampling biases in the unevenly-distributed ITP data and caveats in detection methods. The highest concentration of eddies was found in the western and southern portions of the basin, close to topographic margins and boundaries of the Beaufort Gyre. The number of lower halocline eddies approximately doubled from 2005-2012 to 2013-2014. The increased eddy density suggests more active baroclinic instability of the Beaufort Gyre that releases available potential energy to balance the wind-energy input; this may stabilize the Gyre spin up and associated freshwater increase.

Description: After several years of decreased annual rainfall and water shortages, the Chilean society is demanding that forest plantations take accountability of their role in consuming scarce water resources. Evidence has shown that interception losses are considerable when determining water production in watersheds. The aim of this study was to determine if site and stand variables explain interception losses by Chilean forests for the development of an empirical model that could predict the potential impacts of forest management practices and land-use change. A total of 127 data from annual water balance plot studies in Chile were compiled to derive relationships between interception and precipitation, species composition, plantation age and other stand and site variables. The reviewed data indicated that annual interception losses are mainly explained by annual rainfall and basal area of the forest stands, with a clear difference between the northern (dryer) and southern (wetter) regions of Chile. For a wide latitudinal gradient, forest composition and age, annual interception accounted for approximately 21% of incoming precipitations. Broadleaved forest stands (including native broadleaved and eucalypt forests) generally presented higher interception losses than conifers. Interception was higher in northern zones indicating that forests have greater impacts on water resources in dryer regions. Our results were compiled in empirical models, which can be used to estimate forest interception in a latitudinal gradient in Chile and to support policy making. These results are also proposed as an approximate analogue of the changes in forest interception losses which may occur as vegetation belts shift latitudinally due to the impact of climate change.

Description: Abstract The Arctic Ocean mixed layer interacts with the ice cover above and warmer, nutrient rich waters below. Ice‐Tethered Profiler observations in the Canada Basin of the Arctic Ocean over 2006‐2017 are used to investigate changes in mixed layer properties. In contrast to decades of shoaling since at least the 1980's, the mixed layer deepened by 9 m from 2006‐2012 to 2013‐2017. Deepening resulted from an increase in mixed layer salinity that also weakened stratification at the base of the mixed layer. Vertical mixing alone can explain less than half of the observed change in mixed layer salinity, and so the observed increase in salinity is inferred to result from changes in freshwater accumulation via changes to ice‐ocean circulation or ice melt/growth and river runoff. Even though salinity increased, the shallowest density surfaces deepened by 5 m on average suggesting that Ekman pumping over this time period remained downwards. A deeper mixed layer with weaker stratification has implications for the accessibility of heat and nutrients stored in the upper halocline. The extent to which the mixed layer will continue to deepen appears to depend primarily on the complex set of processes influencing freshwater accumulation.

Description: Abstract Convective organization has a large impact on precipitation and feeds back on larger‐scale circulations in the tropics. The degree of this convective organization changes with modes of climate variability like the El Niño Southern Oscillation (ENSO), but because organization is not represented in current climate models, a quantitative assessment of these shifts has not been possible. Here, we construct multi‐decade satellite climatologies of occurrence of tropical convective organization and its properties and assess changes with ENSO phase. The occurrence of organized deep convection becomes more concentrated, increasing 3‐fold in the Eastern and Central Pacific during El Niño and decreasing 2‐fold outside of these regions. Both horizontal extent of the cold cloud shield and convective depth increase in regions of positive SSTa; however, the regions of greatest convective deepening are those of large‐scale ascent, rather than those of warmest SSTa. Extent decreases with SSTa at a rate of about 20 km K‐1, while the SSTa dependence of depth is only about 0.2 K K‐1. We introduce two values to describe convective changes with ENSO more succinctly: (1) an information entropy metric to quantify the clustering of convective system occurrences and (2) a growth metric to quantify deepening relative to spreading over the system lifetime. Finally, with collocated precipitation data, we see that rainfall attributable to convective organization jumps up to 5% with warming. Rain intensity and amount increase for a given system size during El Niño, but a given rain amount may actually fall with higher intensity during La Niña.

Description: Abstract The D/H ratio of epicuticular plant waxes (δDwax) preserved in sedimentary archives is a powerful tool for paleoclimate reconstruction, but comparisons to other proxy records or to climate model simulations requires a Proxy System Model (PSM) that accounts for transformations between δDprecip and δDwax. Here, we present a new, publicly available PSM for plant waxes, WaxPSM. WaxPSM predicts δDwax from observational data or any modern, paleo, or future climate model experiment. δD values of the C29 n‐alkane are calculated based on precipitation or soil water δD and observed apparent fractionation values, adjusted for plant‐type differences. Using WaxPSM, we assess three key uncertainties in δDwax records: the degree to which variations in δD may reflect changes in vegetation rather than climate; structural uncertainties that arise from limited water isotopic observations; and the impacts of land cover change on climate reconstructions during the Last Glacial Maximum and the Pre‐Industrial period. Parametric and structural uncertainties can cause δDwax variations up to 50‰, but in most cases the differences are ∼10‐30‰. The drier subtropics are additionally impacted by the incorrect structural assumption that plants' source water, δDsoil, is isotopically similar to the climate variable of interest, δDprecip. We recommend a coordinated, systematic effort to elevate observational constraints on δDprecip, δDsoil, and the δD of multiple compound classes, which would dramatically reduce parametric and structural uncertainties and allow further complexity to be built into the model.

Description: Abstract Questions Vegetation‐plot records provide information on presence and cover or abundance of plants co‐occurring in the same community. Vegetation‐plot data are spread across research groups, environmental agencies and biodiversity research centers and, thus, are rarely accessible at continental or global scales. Here we present the sPlot database, which collates vegetation plots worldwide to allow for the exploration of global patterns in taxonomic, functional and phylogenetic diversity at the plant community level. Location sPlot version 2.1 contains records from 1,121,244 vegetation plots, which comprise 23,586,216 records of plant species and their relative cover or abundance in plots collected between 1885 and 2015. Methods We complemented the information for each plot by retrieving climate and soil conditions and the biogeographic context (e.g. biomes) from external sources, and by calculating community‐weighted means and variances of traits using gap‐filled data from the global plant trait database TRY. Moreover, we created a phylogenetic tree for 50,167 out of the 54,519 species identified in the plots. Results We present the first maps of global patterns of community richness and community‐weighted means of key traits. Conclusions The availability of vegetation plot data in sPlot offers new avenues for vegetation analysis at the global scale. This article is protected by copyright. All rights reserved.

Description: Limnology and Oceanography Bulletin, Volume 28, Issue 1, Page 26-30, February 2019.