Ocean mover's distance: using optimal transport for analysing oceanographic data.

Remote sensing observations from satellites and global biogeochemical models have combined to revolutionize the study of ocean biogeochemical cycling, but comparing the two data streams to each other and across time remains challenging due to the strong spatial-temporal structuring of the ocean. Here, we show that the Wasserstein distance provides a powerful metric for harnessing these structured datasets for better marine ecosystem and climate predictions. The Wasserstein distance complements commonly used point-wise difference methods such as the root-mean-squared error, by quantifying differences in terms of spatial displacement in addition to magnitude. As a test case, we consider chlorophyll (a key indicator of phytoplankton biomass) in the northeast Pacific Ocean, obtained from model simulations, in situ measurements, and satellite observations. We focus on two main applications: (i) comparing model predictions with satellite observations, and (ii) temporal evolution of chlorophyll both seasonally and over longer time frames. The Wasserstein distance successfully isolates temporal and depth variability and quantifies shifts in biogeochemical province boundaries. It also exposes relevant temporal trends in satellite chlorophyll consistent with climate change predictions. Our study shows that optimal transport vectors underlying the Wasserstein distance provide a novel visualization tool for testing models and better understanding temporal dynamics in the ocean.

Egg incubation temperature influences the population-specific outmigration rate of juvenile brown trout Salmo trutta.

The present experiment tested if temperature during embryogenesis and parental heritage affected the migratory behaviour of young brown trout Salmo trutta. Two parental forms were used, a freshwater resident form and an anadromous form, both from the same river system but geographically isolated since 1993-95. Four groups of young S. trutta were produced and reared from (a) freshwater resident parents spawning in a tributary to the River Imsa, Norway, (b) anadromous parents spawning in the main stem of the same river system, (c) resident male × anadromous female parents and (d) resident female × anadromous male parents. The eggs were incubated until first exogenous feeding in River Imsa water, either unheated or heated c. 2.7°C above ambient temperature. Thereafter, all fish experienced the same ambient river temperature until release. Groups were released below an impassable waterfall 900 m upstream of the mouth of the River Imsa, either as age-0 in October 2019 or as age-1 in May 2020. About 7.5% of the released fish moved downstream and were captured in a trap at the outlet. For any given body size, the proportion of warm incubated trout that moved downstream was greater than the proportion of cold incubated trout. It was also found that most emigrants of the October-released S. trutta were caught within a month of release. Also, most May-released S. trutta emigrated in October. The offspring of the freshwater resident parents emigrated to a larger extent than offspring of anadromous parents. Thus, the difference in emigration with regard to embryonic temperature was phenotypically plastic and may be associated with an epigenetic effect of the thermal conditions during early development. The effect of parental origin suggests there may be genetic divergence between the geographically isolated populations.

Differences in growth between offspring of anadromous and freshwater brown trout Salmo trutta.

In this study, individual growth of juvenile offspring of anadromous and freshwater resident brown trout Salmo trutta and crosses between the two from the River Imsa, Norway, was estimated. The juveniles were incubated until hatching at two temperatures (±S.D.), either 4.4 ± 1.5°C or 7.1 ± 0.6°C. Growth rate was estimated for 22 days in August-September when the fish on average were c. 8 g in wet mass, and the estimates were standardized to 1 g fish dry mass. Offspring of anadromous S. trutta grew better at both 15 and 18°C than offspring of freshwater resident S. trutta or offspring of crosses between the two S. trutta types. This difference appears not to result from a maternal effect because anadromous S. trutta grew better than the hybrids with anadromous mothers. Instead, this appears to be an inherited difference between the anadromous and the freshwater resident fish lending support to the hypothesis that anadromous and freshwater resident S. trutta in this river differ in genetic expression. Egg incubation temperature of S. trutta appeared not to influence the later growth as reported earlier from the studies of Atlantic salmon Salmo salar.

Continuous outmigration and sequential encountering of environmental cues are important for successful homing of hatchery-reared, anadromous brown trout Salmo trutta.

When rehabilitating and reintroducing trout Salmo trutta in rivers, it is a goal that as many as possible survive, home and form self-sustaining populations. Hatchery-reared, anadromous S. trutta have significant lower ability to return to the area where they were raised if (a) transported in a closed tank to sea and released 5 km from the River Imsa, relative to those that were (b) transported when swimming in a partly submerged tank with sea water run-through, while being slowly towed by a boat the same distance or (c) released at the outlet of the River Imsa. Thus, if deprived from environmental cues during part of the way, they lose their ability to home.

Controls on surface water carbonate chemistry along North American ocean margins.

Syntheses of carbonate chemistry spatial patterns are important for predicting ocean acidification impacts, but are lacking in coastal oceans. Here, we show that along the North American Atlantic and Gulf coasts the meridional distributions of dissolved inorganic carbon (DIC) and carbonate mineral saturation state (Ω) are controlled by partial equilibrium with the atmosphere resulting in relatively low DIC and high Ω in warm southern waters and the opposite in cold northern waters. However, pH and the partial pressure of CO2 (pCO2) do not exhibit a simple spatial pattern and are controlled by local physical and net biological processes which impede equilibrium with the atmosphere. Along the Pacific coast, upwelling brings subsurface waters with low Ω and pH to the surface where net biological production works to raise their values. Different temperature sensitivities of carbonate properties and different timescales of influencing processes lead to contrasting property distributions within and among margins.

Egg incubation temperature affects the timing of the Atlantic salmon Salmo salar homing migration.

Here, we show that adult Atlantic salmon Salmo salar returned about 2 weeks later from the feeding areas in the North Atlantic Ocean to the Norwegian coast, through a phenotypically plastic mechanism, when they developed as embryos in c. 3°C warmer water than the regular incubation temperature. This finding has relevance to changes in migration timing caused by climate change and for cultivation and release of S. salar.

Large-scale ocean connectivity and planktonic body size.

Global patterns of planktonic diversity are mainly determined by the dispersal of propagules with ocean currents. However, the role that abundance and body size play in determining spatial patterns of diversity remains unclear. Here we analyse spatial community structure - ß-diversity - for several planktonic and nektonic organisms from prokaryotes to small mesopelagic fishes collected during the Malaspina 2010 Expedition. ß-diversity was compared to surface ocean transit times derived from a global circulation model, revealing a significant negative relationship that is stronger than environmental differences. Estimated dispersal scales for different groups show a negative correlation with body size, where less abundant large-bodied communities have significantly shorter dispersal scales and larger species spatial turnover rates than more abundant small-bodied plankton. Our results confirm that the dispersal scale of planktonic and micro-nektonic organisms is determined by local abundance, which scales with body size, ultimately setting global spatial patterns of diversity.

Rapid warming and salinity changes in the Gulf of Maine alter surface ocean carbonate parameters and hide ocean acidification.

A profound warming event in the Gulf of Maine during the last decade has caused sea surface temperatures to rise to levels exceeding any earlier observations recorded in the region over the last 150 years. This event dramatically affected CO2 solubility and, in turn, the status of the sea surface carbonate system. When combined with the concomitant increase in sea surface salinity and assumed rapid equilibration of carbon dioxide across the air sea interface, thermodynamic forcing partially mitigated the effects of ocean acidification for pH, while raising the saturation index of aragonite ( Ω AR ) by an average of 0.14 U. Although the recent event is categorically extreme, we find that carbonate system parameters also respond to interannual and decadal variability in temperature and salinity, and that such phenomena can mask the expression of ocean acidification caused by increasing atmospheric carbon dioxide. An analysis of a 34-year salinity and SST time series (1981-2014) shows instances of 5-10 years anomalies in temperature and salinity that perturb the carbonate system to an extent greater than that expected from ocean acidification. Because such conditions are not uncommon in our time series, it is critical to understand processes controlling the carbonate system and how ecosystems with calcifying organisms respond to its rapidly changing conditions. It is also imperative that regional and global models used to estimate carbonate system trends carefully resolve variations in the physical processes that control CO2 concentrations in the surface ocean on timescales from episodic events to decades and longer.

Gene flow from domesticated escapes alters the life history of wild Atlantic salmon.

Interbreeding between domesticated and wild animals occurs in several species. This gene flow has long been anticipated to induce genetic changes in life-history traits of wild populations, thereby influencing population dynamics and viability. Here, we show that individuals with high levels of introgression (domesticated ancestry) have altered age and size at maturation in 62 wild Atlantic salmon Salmo salar populations, including seven ancestral populations to breeding lines of the domesticated salmon. This study documents widespread changes to life-history traits in wild animal populations following gene flow from selectively bred, domesticated conspecifics. The continued high abundance of escaped, domesticated Atlantic salmon thus threatens wild Atlantic salmon populations by inducing genetic changes in fitness-related traits. Our results represent key evidence and a timely warning concerning the potential ecological impacts of the globally increasing use of domesticated animals.

The timescales of global surface-ocean connectivity.

Planktonic communities are shaped through a balance of local evolutionary adaptation and ecological succession driven in large part by migration. The timescales over which these processes operate are still largely unresolved. Here we use Lagrangian particle tracking and network theory to quantify the timescale over which surface currents connect different regions of the global ocean. We find that the fastest path between two patches--each randomly located anywhere in the surface ocean--is, on average, less than a decade. These results suggest that marine planktonic communities may keep pace with climate change--increasing temperatures, ocean acidification and changes in stratification over decadal timescales--through the advection of resilient types.

An Ultrahigh Precision, High-Frequency Dissolved Inorganic Carbon Analyzer Based on Dual Isotope Dilution and Cavity Ring-Down Spectroscopy.

We present a novel method for continuous and automated shipboard measurements of dissolved inorganic carbon concentration ([DIC]) in surface water. The method is based on dual isotope dilution and cavity ring-down spectroscopy (DID-CRDS). In this method, seawater is continuously sampled and mixed with a flow of NaH(13)CO3 solution that is also enriched in deuterated water (the spike). The isotopic composition of CO2 (δ(13)C(spiked_sample)) derived from the DIC in the mixture, and the D/H ratio of the mixed water (δD(spiked_sample)), are measured by CRDS analyzers. The D/H of the water in the mixture allows accurate estimates of the mixing ratio of the sample and the spike. [DIC] of the sample is then calculated from the mixing ratio, [DI(13)C] of the spike, and δ(13)C(spiked_sample). In the laboratory, the precision of the method is <0.02% (±0.4 µmol kg(-1) when [DIC] = 2000 µmol kg(-1)). A shipboard test was conducted in the Delaware Bay and Estuary. For 2 min average [DIC], a precision of <0.03% was achieved. Measurements from the DID-CRDS showed good agreement with independent measurements of discrete samples using the well-established coulometric method (mean difference = -1.14 ± 1.68 µmol kg(-1)), and the nondispersive infrared(NDIR)-based methods (mean difference = -0.9 ± 4.73 µmol kg(-1)).

Basin-scale phenology and effects of climate variability on global timing of initial seaward migration of Atlantic salmon (Salmo salar).

Migrations between different habitats are key events in the lives of many organisms. Such movements involve annually recurring travel over long distances usually triggered by seasonal changes in the environment. Often, the migration is associated with travel to or from reproduction areas to regions of growth. Young anadromous Atlantic salmon (Salmo salar) emigrate from freshwater nursery areas during spring and early summer to feed and grow in the North Atlantic Ocean. The transition from the freshwater ('parr') stage to the migratory stage where they descend streams and enter salt water ('smolt') is characterized by morphological, physiological and behavioural changes where the timing of this parr-smolt transition is cued by photoperiod and water temperature. Environmental conditions in the freshwater habitat control the downstream migration and contribute to within- and among-river variation in migratory timing. Moreover, the timing of the freshwater emigration has likely evolved to meet environmental conditions in the ocean as these affect growth and survival of the post-smolts. Using generalized additive mixed-effects modelling, we analysed spatio-temporal variations in the dates of downstream smolt migration in 67 rivers throughout the North Atlantic during the last five decades and found that migrations were earlier in populations in the east than the west. After accounting for this spatial effect, the initiation of the downstream migration among rivers was positively associated with freshwater temperatures, up to about 10 °C and levelling off at higher values, and with sea-surface temperatures. Earlier migration occurred when river discharge levels were low but increasing. On average, the initiation of the smolt seaward migration has occurred 2.5 days earlier per decade throughout the basin of the North Atlantic. This shift in phenology matches changes in air, river, and ocean temperatures, suggesting that Atlantic salmon emigration is responding to the current global climate changes.

Effects of temperature and food quality on age and size at maturity in ectotherms: an experimental test with Atlantic salmon.

The reaction norm between growth rate, age and size at maturity in ectotherms is widely debated in ecological literature. It has been proposed that the effect depends on whether growth is affected by food quality or temperature (called the Berrigan-Charnov puzzle). The present experiment tested this for Atlantic salmon (Salmo salar). We enhanced growth rates by increasing temperature and ratio of lipids to proteins in the food for groups of Atlantic salmon. Both treatments gave higher percentages of early mature and therefore smaller adults in contrast to the proposed Berrigan-Charnov puzzle. There was a difference between sexes in that males could attain maturity 1 year younger than females when reared under similar environmental conditions. Males that matured during the first year in sea water were smaller than similar aged immature males. The probability of that Atlantic salmon attained maturity for the first time during their second year in sea increased with growth rate during the preceding winter and if fed a high-lipid diet. Increased summer temperature exhibited no additional effect. Similar aged fish reared at elevated temperature and fed high-lipid diet attained maturity at a larger body mass and exhibited higher mass-length-ratios than those reared at natural temperature and fed a low-lipid diet, indicating that structural growth has priority over lipid deposits. Increased growth rate before the onset of maturation, whether this is owing to enhanced lipid content in food or increased water temperature, decreased age and therefore size at maturity. Enhanced lipid relative to protein content in food, but not temperature, had an additive positive effect on early maturation probability, likely due to increased amounts of reserve energy. These results may be general for ectotherm organisms.

Marine ecosystem modeling beyond the box: using GIS to study carbon fluxes in a coastal ecosystem.

Studies of carbon fluxes in marine ecosystems are often done by using box model approaches with basin size boxes, or highly resolved 3D models, and an emphasis on the pelagic component of the ecosystem. Those approaches work well in the ocean proper, but can give rise to considerable problems when applied to coastal systems, because of the scale of certain ecological niches and the fact that benthic organisms are the dominant functional group of the ecosystem. In addition, 3D models require an extensive modeling effort. In this project, an intermediate approach based on a high resolution (20x20 m) GIS data-grid has been developed for the coastal ecosystem in the Laxemar area (Baltic Sea, Sweden) based on a number of different site investigations. The model has been developed in the context of a safety assessment project for a proposed nuclear waste repository, in which the fate of hypothetically released radionuclides from the planned repository is estimated. The assessment project requires not only a good understanding of the ecosystem dynamics at the site, but also quantification of stocks and flows of matter in the system. The data-grid was then used to set up a carbon budget describing the spatial distribution of biomass, primary production, net ecosystem production and thus where carbon sinks and sources are located in the area. From these results, it was clear that there was a large variation in ecosystem characteristics within the basins and, on a larger scale, that the inner areas are net producing and the outer areas net respiring, even in shallow phytobenthic communities. Benthic processes had a similar or larger influence on carbon fluxes as advective processes in inner areas, whereas the opposite appears to be true in the outer basins. As many radionuclides are expected to follow the pathways of organic matter in the environment, these findings enhance our abilities to realistically describe and predict their fate in the ecosystem.

Human modification of global water vapor flows from the land surface.

It is well documented that human modification of the hydrological cycle has profoundly affected the flow of liquid water across the Earth's land surface. Alteration of water vapor flows through land-use changes has received comparatively less attention, despite compelling evidence that such alteration can influence the functioning of the Earth System. We show that deforestation is as large a driving force as irrigation in terms of changes in the hydrological cycle. Deforestation has decreased global vapor flows from land by 4% (3,000 km(3)/yr), a decrease that is quantitatively as large as the increased vapor flow caused by irrigation (2,600 km(3)/yr). Although the net change in global vapor flows is close to zero, the spatial distributions of deforestation and irrigation are different, leading to major regional transformations of vapor-flow patterns. We analyze these changes in the light of future land-use-change projections that suggest widespread deforestation in sub-Saharan Africa and intensification of agricultural production in the Asian monsoon region. Furthermore, significant modification of vapor flows in the lands around the Indian Ocean basin will increase the risk for changes in the behavior of the Asian monsoon system. This analysis suggests that the need to increase food production in one region may affect the capability to increase food production in another. At the scale of the Earth as a whole, our results emphasize the need for climate models to take land-use change, in both land cover and irrigation, into account.

Baltic sub-basin turnover times examined using the Rossby Centre Ocean model.

Not least when judging the possible effects of climate change it proves necessary to estimate the water-renewal rates of limited marine areas subject to pronounced external influences. In connection with the SWECLIM programme this has been undertaken for two ecologically sensitive sub-basins of the Baltic, viz. the Gulf of Riga and Gdansk Bay. For this purpose two methodologically different approaches have been employed, based on mass-balance budgets and analysis of Lagrangian trajectories, respectively. When compared to the results obtained using the Lagrangian technique, the box-model approach proved to be adequate for the Gulf of Riga representing a morphologically highly constrained basin, whereas it demonstrated certain shortcomings when applied to the more open topographic conditions characterizing Gdansk Bay.

Resource utilization of sympatric and experimentally allopatric cutthroat trout and Dolly Varden charr.

Resource utilization by cutthroat trout (CT) and Dolly Varden charr (DV) was studied 8 years after experimental transfers from sympatry had established reproducing allopatric populations in two nearby fishless lakes. Allopatric DV significantly increased their utilization of shallow-dwelling zoobenthos, and increased their vertical distribution in comparison to that in sympatry. In contrast, allopatric CT showed little change in the proportions of major prey types utilized, and, if anything, restricted their vertical distribution in comparison to that in sympatry. The results can be explained by the hypothesis that the resource use of DV is strongly influenced by interspecific competition from CT, whereas CT largely remains unaffected by this interaction. An alternative hypothesis, that lake differences can explain the differences in resource use between sympatry and allopatry, was evaluated by comparing food resource availability and other biotic and abiotic characteristics of the three study lakes. None of these could account for the shift in resource use by DV between sympatry and allopatry, but lake differences may explain why allopatric CT showed a restricted habitat use in comparison with their sympatric donor stock. The results of this whole-lake transfer experiment are consistent with earlier reported field and laboratory studies, and suggest that the aggressive dominance of CT is the most important mechanism by which DV are displaced from littoral and near-surface habitats in sympathy with CT.