The interior spreading story of Labrador Sea Water

The unique convective anomalies of Labrador Sea Water (LSW) can be used as advective tracers when assessing equatorward spreading pathways and timescales of LSW. In this study, we explore advective pathways of two LSW classes formed in the 1990s and early 2000s, respectively, along constant neutral density planes. Hydrographic observations showcase the prevalence of both LSW classes within the Atlantic interior, supporting a recirculation feature that branches from the Deep Western Boundary Current (DWBC) at 36°N among other pathways. Spreading characteristics of both LSW classes from the Labrador Sea to the subtropics are reinforced through a spatial pattern analysis of salinity anomalies and geostrophic velocities along the characteristic neutral density planes of each respective LSW class. We observe both classes to advect out of the Labrador Sea to (i) the eastern subpolar region and down the eastern boundary towards the Atlantic interior, (ii) directly into the Atlantic interior likely from an injection by recirculations from the subpolar gyre and DWBC leakage, and (iii) equatorward along the western boundary via the DWBC. Findings highlight the abundance of LSW within the Atlantic interior, not just along the western boundary, suggesting that interior pathways play an influential role on the export of these subpolar climate signals

Global urban environmental change drives adaptation in white clover

Urbanization transforms environments in ways that alter biological evolution. We examined whether urban environmental change drives parallel evolution by sampling 110,019 white clover plants from 6169 populations in 160 cities globally. Plants were assayed for a Mendelian antiherbivore defense that also affects tolerance to abiotic stressors. Urban-rural gradients were associated with the evolution of clines in defense in 47% of cities throughout the world. Variation in the strength of clines was explained by environmental changes in drought stress and vegetation cover that varied among cities. Sequencing 2074 genomes from 26 cities revealed that the evolution of urban-rural clines was best explained by adaptive evolution, but the degree of parallel adaptation varied among cities. Our results demonstrate that urbanization leads to adaptation at a global scale

Interannual to decadal sea level variability in the subpolar North Atlantic:the role of propagating signals

The gyre-scale, dynamic sea surface height (SSH) variabilitysignifies the spatial redistribution of heat and freshwater in the ocean,influencing the ocean circulation, weather, climate, sea level, andecosystems. It is known that the first empirical orthogonal function (EOF)mode of the interannual SSH variability in the North Atlantic exhibits atripole gyre pattern, with the subtropical gyre varying out of phase withboth the subpolar gyre and the tropics, influenced by the low-frequencyNorth Atlantic Oscillation. Here, we show that the first EOF mode explainsthe majority (60 %-90 %) of the interannual SSH variance in the Labrador andIrminger Sea, whereas the second EOF mode is more influential in thenortheastern part of the subpolar North Atlantic (SPNA), explaining up to60 %-80 % of the regional interannual SSH variability. We find that the twoleading modes do not represent physically independent phenomena. On thecontrary, they evolve as a quadrature pair associated with a propagation ofSSH anomalies from the eastern to the western SPNA. This is confirmed by thecomplex EOF analysis, which can detect propagating (as opposed tostationary) signals. The analysis shows that it takes about 2 years for sealevel signals to propagate from the Iceland Basin to the Labrador Sea, andit takes 7-10 years for the entire cycle of the North Atlantic SSH tripoleto complete. The observed westward propagation of SSH anomalies is linked toshifting wind forcing patterns and to the cyclonic pattern of the mean oceancirculation in the SPNA. The analysis of regional surface buoyancy fluxes incombination with the upper-ocean temperature and salinity changes suggests atime-dependent dominance of either air-sea heat fluxes or advection indriving the observed SSH tendencies, while the contribution of surfacefreshwater fluxes (precipitation and evaporation) is negligible. Wedemonstrate that the most recent cooling and freshening observed in the SPNAsince about 2010 were mostly driven by advection associated with the NorthAtlantic Current. The results of this study indicate that signal propagationis an important component of the North Atlantic SSH tripole, as it appliesto the SPNA

Inferring Advective Timescales and Overturning Pathways of the Deep Western Boundary Current in the North Atlantic Through Labrador Sea Water Advection

The Subpolar North Atlantic plays a critical role in the formation of the deep water masses which drive Atlantic Meridional Overturning Circulation (AMOC). Labrador Sea Water (LSW) is formed in the Labrador Sea and exported predominantly via the Deep Western Boundary Current (DWBC). The DWBC is an essential component of the AMOC advecting deep waters southward, flowing at depth along the continental slope of the western Atlantic. By combining sustained hydrographic observations from the Labrador Sea to 26.5 degrees N, we investigate the signal propagation and advective timescales of LSW via the DWBC from its source region to the Tropical Atlantic through various approaches using robust neutral density classifications. Two individually defined LSW classes are observed to advect on timescales that support a new plausible hydrographically observed advective pathway. We find each LSW class to advect on independent timescales, and validate a hypothesized alternative-interior advection pathway branching from the DWBC by observing the arrival of LSW outside of the DWBC in the Bermuda basin on timescales similar to arriving at 26.5 degrees N, 10-15 yr after leaving the source region. Advective timescales estimated herein indicate that this interior pathway is likely the main advective pathway; it remains uncertain whether a direct pathway plays a significant advective role. Using LSW convective signals as advective tracers along the DWBC permits the estimation of advective timescales from the subpolar to tropical latitudes, illuminating deep water advection pathways across the North Atlantic and the lower-limb of AMOC as a whole.Plain Language Summary The Deep Western Boundary Current (DWBC) exports cold and dense deep waters formed in the Subpolar North Atlantic to the tropics, and therefore plays a primary role in global ocean circulation and heat balance. We focus here on Labrador Sea Water (LSW), a water mass formed through wintertime mixing events within the Subpolar North Atlantic characterized by distinctive low-temperature and low-salinity signatures. By following the passage of these signatures through several locations, we investigate the pathways and spreading timescales of LSW from its source region toward the subtropical North Atlantic by the DWBC. We find two distinct LSW masses to reach the same location on independent timescales, and observe LSW in the Central Atlantic just prior to or on the same timescale as being observed in the Tropical Atlantic. These findings indicate that an alternative-interior export pathway branching from the DWBC is likely to exist, exporting LSW away from the continental slope and into the Atlantic interior rather than following a direct equatorward route. Estimating advective timescales and pathways of the DWBC using LSW aid in the present understanding and future prediction of overturning circulation in the Atlantic Ocean

Global Oceans

The Atlantic meridional overturning circulation (MOC) and heat transport (MHT) have been observed (Fig. 3.21) at several trans-basin and western boundary moored arrays (e.g., Frajka-Williams et al. 2019; Berx et al. 2021; Hummels et al. 2022), as well as by synthesizing in situ and satellite altimetry measurements at several latitudes (Hobbs and Willis 2012; Sanchez-Franks et al. 2021; Dong et al. 2021; Kersalé et al. 2021). Here we provide updates on the MOC and MHT estimates from the Rapid Climate Change/MOC and Heatflux Array/Western Boundary Time Series (RAPID-MOCHA-WBTS) moored array at 26.5°N and from the synthetic approach at 41°N and at several latitudes in the South Atlantic. While updates for the Overturning in the Subpolar North Atlantic Program and the South Atlantic MOC Basin-wide Array at 34.5°S are pending, we report on recent advances in observing the variability of flows comprising the lower limb of the North Atlantic MOC, including the Meridional Overturning Variability Experiment (MOVE, 16°N)

Global urban environmental change drives adaptation in white clover.

Urbanization transforms environments in ways that alter biological evolution. We examined whether urban environmental change drives parallel evolution by sampling 110,019 white clover plants from 6169 populations in 160 cities globally. Plants were assayed for a Mendelian antiherbivore defense that also affects tolerance to abiotic stressors. Urban-rural gradients were associated with the evolution of clines in defense in 47% of cities throughout the world. Variation in the strength of clines was explained by environmental changes in drought stress and vegetation cover that varied among cities. Sequencing 2074 genomes from 26 cities revealed that the evolution of urban-rural clines was best explained by adaptive evolution, but the degree of parallel adaptation varied among cities. Our results demonstrate that urbanization leads to adaptation at a global scale

Global urban environmental change drives adaptation in white clover

Urbanization transforms environments in ways that alter biological evolution. We examined whether urban environmental change drives parallel evolution by sampling 110,019 white clover plants from 6169 populations in 160 cities globally. Plants were assayed for a Mendelian antiherbivore defense that also affects tolerance to abiotic stressors. Urban-rural gradients were associated with the evolution of clines in defense in 47% of cities throughout the world. Variation in the strength of clines was explained by environmental changes in drought stress and vegetation cover that varied among cities. Sequencing 2074 genomes from 26 cities revealed that the evolution of urban-rural clines was best explained by adaptive evolution, but the degree of parallel adaptation varied among cities. Our results demonstrate that urbanization leads to adaptation at a global scale

Global urban environmental change drives adaptation in white clover

Urbanization transforms environments in ways that alter biological evolution. We examined whether urban environmental change drives parallel evolution by sampling 110,019 white clover plants from 6169 populations in 160 cities globally. Plants were assayed for a Mendelian antiherbivore defense that also affects tolerance to abiotic stressors. Urban-rural gradients were associated with the evolution of clines in defense in 47% of cities throughout the world. Variation in the strength of clines was explained by environmental changes in drought stress and vegetation cover that varied among cities. Sequencing 2074 genomes from 26 cities revealed that the evolution of urban-rural clines was best explained by adaptive evolution, but the degree of parallel adaptation varied among cities. Our results demonstrate that urbanization leads to adaptation at a global scale