High-frequency variability in the North Icelandic Jet

Author Posting. © The Authors, 2018. This article is posted here by permission of Sears Foundation for Marine Research for personal use, not for redistribution. The definitive version was published in Journal of Marine Research 76 (2018): 47-62, doi:10.1357/002224018824845910.We describe the high-frequency variability in the North Icelandic Jet (NIJ) on the Iceland Slope using data from the densely instrumented Kögur mooring array deployed upstream of the Denmark Strait sill from September 2011 to July 2012. Significant sub-8-day variability is ubiquitous in all moorings from the Iceland slope with a dominant period of 3.6 days. We attribute this variability to topographic Rossby waves on the Iceland slope with a wavelength of 62 ± 3 km and a phase velocity of 17.3 ± 0.8 km/day−1 directed downslope (−9◦ relative to true-north). We test the theoretical dispersion relation for these waves against our observations and find good agreement between the predicted and measured direction of phase propagation.We additionally calculate a theoretical group velocity of 36 km day−1 directed almost directly up-slope (106◦ relative to true-north) that agrees well with the propagation speed and direction of observed energy pulses. We use an inverse wave tracing model to show that this wave energy is generated locally, offshore of the array, and does not emanate from the upstream or downstream directions along the Iceland slope. It is hypothesized that either the meandering Separated East Greenland Current located seaward of the NIJ or intermittent aspiration of dense water into the Denmark Strait Overflow are the drivers of the topographic waves.This work was supported by National Science Foundation grants OCE-1433958 (BH), OCE-0959381 (BH and RP) and OCE-1558742 (RP)

Moored observations of synoptic and seasonal variability in the East Greenland Coastal Current

Author Posting. © American Geophysical Union, 2014. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 119 (2014): 8838–8857, doi:10.1002/2014JC010134.We present a year-round assessment of the hydrographic variability within the East Greenland Coastal Current on the Greenland shelf from five synoptic crossings and 4 years of moored hydrographic data. From the five synoptic sections the current is observed as a robust, surface intensified flow with a total volume transport of 0.66 ± 0.18 Sv and a freshwater transport of 42 ± 12 mSv. The moorings showed heretofore unobserved variability in the abundance of Polar and Atlantic water masses in the current on synoptic scales. This is exhibited as large vertical displacement of isotherms (often greater than 100 m). Seasonally, the current is hemmed into the coast during the fall by a full depth Atlantic Water layer that has penetrated onto the inner shelf. The Polar Water layer in the current then thickens through the winter and spring seasons increasing the freshwater content in the current; the timing implies that this is probably driven by the seasonally varying export of freshwater from the Arctic and not the local runoff from Greenland. The measured synoptic variability is enhanced during the winter and spring period due to a lower halocline and a concurrent enhancement in the along-coast wind speed. The local winds force much of the high-frequency variability in a manner consistent with downwelling, but variability distinct from downwelling is also visible.This work was funded by the National Science Foundation grant OCE-1130008, NASA grant NNX13AK88G, and the Ocean and Climate Change Institute at the Woods Hole Oceanographic Institution.2015-06-2

Trends in physical properties at the southern New England shelf break

Author Posting. © American Geophysical Union, 2020. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research-Oceans 125(2), (2020): e2019JC015784, doi:10.1029/2019JC015784.We analyze 11 years (2003–2013) of repeat temperature and salinity sections from across the New England shelf break south of Cape Cod during early summer (June–July). The mean sections resolved the shelf break front which supports the Shelf Break Jet, a vital component of the regional circulation. Individual sections showed a great deal of variability associated with meanders in the shelf break front consistent with previous studies in the region. Over the 11 year record, the shelf region (inshore of the 100 m isobath) warmed by 0.26 °C yr -1, with the majority of this warming occurring shallower than 20 m (0.58 °C yr -1). The full‐depth trend agrees well with previous studies of shelf warming to the north and the south of our study region. The temperature and salinity of the offshore edge of the Cold Pool Water on the shelf did not change significantly during this period. The surface warming on the shelf resulted in a decrease in near‐surface density of 0.12 kg m -3 yr -1 and an increase in stratification between 10 and 15 m of 6.7 X 10(-5) S -2 yr -1 . Offshore of the shelf break, the Slope Water also warmed and became more saline by 0.21 °C yr -1 and 0.04 yr -1 respectively, resulting in a maximal reduction in density of 0.01 kg m -3 yr -1. In the Shelf Break Front, there is some evidence of freshening and a reduction in density, which may have resulted from an offshore shift in the Cold Pool but the statistical significance is small.We wish to thank the Sea Education Association and the Woods Hole Oceanographic Institution for maintaining this collaboration. We also extend our warmest thanks to the numerous chief scientists, crew members, and student participants who collected the data and made this work possible. This work was supported by NSF Grants OCE‐1657853 and OCE‐1851261. G. G. was also supported by a Senior Scientist Chair from the Woods Hole Oceanographic Institution. The Jake Peirson Summer Cruises were supported using funds provided by a WHOI‐MIT Joint Program alumnus and by the WHOI Academic Programs Office. M. I. was supported by The Woods Hole Partnership Education Program, the Sea Education Association, and the Woods Hole Oceanographic Institution for her summer research work. We thank Jacob Forsyth for discussions on the seasonal variability of warming over the New Jersey shelf and warming rates for different time frames. Data used in this paper are available from the WHOI‐MBL Library (https://darchive.mblwhoilibrary.org/handle/1912/25158, doi:10.26025/dz4w‐kk13)

Composition and variability of the Denmark Strait Overflow Water in a high-resolution numerical model hindcast simulation

Author Posting. © American Geophysical Union, 2017. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 122 (2017): 2830–2846, doi:10.1002/2016JC012158.The upstream sources and pathways of the Denmark Strait Overflow Water and their variability have been investigated using a high-resolution model hindcast. This global simulation covers the period from 1948 to 2009 and uses a fine model mesh (1/20°) to resolve mesoscale features and the complex current structure north of Iceland explicitly. The three sources of the Denmark Strait Overflow, the shelfbreak East Greenland Current (EGC), the separated EGC, and the North Icelandic Jet, have been analyzed using Eulerian and Lagrangian diagnostics. The shelfbreak EGC contributes the largest fraction in terms of volume and freshwater transport to the Denmark Strait Overflow and is the main driver of the overflow variability. The North Icelandic Jet contributes the densest water to the Denmark Strait Overflow and shows only small temporal transport variations. During summer, the net volume and freshwater transports to the south are reduced. On interannual time scales, these transports are highly correlated with the large-scale wind stress curl around Iceland and, to some extent, influenced by the North Atlantic Oscillation, with enhanced southward transports during positive phases. The Lagrangian trajectories support the existence of a hypothesized overturning loop along the shelfbreak north of Iceland, where water carried by the North Icelandic Irminger Current is transformed and feeds the North Icelandic Jet. Monitoring these two currents and the region north of the Iceland shelfbreak could provide the potential to track long-term changes in the Denmark Strait Overflow and thus also the AMOC.Norwegian Research Council Grant Number: 2316472017-10-0

Structure and variability of the shelfbreak East Greenland Current north of Denmark Strait

Author Posting. © American Meteorological Society, 2017. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 47 (2017): 2631-2646, doi:10.1175/JPO-D-17-0062.1.Data from a mooring array deployed north of Denmark Strait from September 2011 to August 2012 are used to investigate the structure and variability of the shelfbreak East Greenland Current (EGC). The shelfbreak EGC is a surface-intensified current situated just offshore of the east Greenland shelf break flowing southward through Denmark Strait. This study identified two dominant spatial modes of variability within the current: a pulsing mode and a meandering mode, both of which were most pronounced in fall and winter. A particularly energetic event in November 2011 was related to a reversal of the current for nearly a month. In addition to the seasonal signal, the current was associated with periods of enhanced eddy kinetic energy and increased variability on shorter time scales. The data indicate that the current is, for the most part, barotropically stable but subject to baroclinic instability from September to March. By contrast, in summer the current is mainly confined to the shelf break with decreased eddy kinetic energy and minimal baroclinic conversion. No other region of the Nordic Seas displays higher levels of eddy kinetic energy than the shelfbreak EGC north of Denmark Strait during fall. This appears to be due to the large velocity variability on mesoscale time scales generated by the instabilities. The mesoscale variability documented here may be a source of the variability observed at the Denmark Strait sill.Support for this work was provided by the Norwegian Research Council under Grant Agreement 231647 (LH and KV) and the Bergen Research Foundation under Grant BFS2016REK01 (KV). Additional funding was provided by the National Science Foundation under Grants OCE-0959381 and OCE-1558742 (RP)

Land Use and Land Cover Affect the Depth Distribution of Soil Carbon: Insights From a Large Database of Soil Profiles

Soils contain a large and dynamic fraction of global terrestrial carbon stocks. The distribution of soil carbon (SC) with depth varies among ecosystems and land uses and is an important factor in calculating SC stocks and their vulnerabilities. Systematic analysis of SC depth distributions across databases of SC profiles has been challenging due to the heterogeneity of soil profile measurements, which vary in depth sampling. Here, we fit over 40,000 SC depth profiles to an exponential decline relationship with depth to determine SC concentration at the top of the mineral soil, minimum SC concentration at depth, and the characteristic “length” of SC concentration decline with depth. Fitting these parameters allowed profile characteristics to be analyzed across a large and heterogeneous dataset. We then assessed the differences in these depth parameters across soil orders and land cover types and between soil profiles with or without a history of tillage, as represented by the presence of an Ap horizon. We found that historically tilled soils had more gradual decreases of SC with depth (greater e-folding depth or Z∗), deeper SC profiles, lower SC concentrations at the top of the mineral soil, and lower total SC stocks integrated to 30 cm. The large database of profiles allowed these results to be confirmed across different land cover types and spatial areas within the Continental United States, providing robust evidence for systematic impacts of historical tillage on SC stocks and depth distributions

Upstream sources of the Denmark Strait Overflow : observations from a high-resolution mooring array

© The Author(s), 2016. This is the author's version of the work and is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Deep Sea Research Part I: Oceanographic Research Papers 112 (2016): 94-112, doi:10.1016/j.dsr.2016.02.007.We present the first results from a densely instrumented mooring array upstream of the Denmark Strait sill, extending from the Iceland shelfbreak to the Greenland shelf. The array was deployed from September 2011 to July 2012, and captured the vast majority of overflow water denser than 27.8 kgm-3 approaching the sill. The mean transport of overflow water over the length of the deployment was 3.54 ± 0.16 Sv. Of this, 0.58 Sv originated from below sill depth, revealing that aspiration takes place in Denmark Strait. We confirm the presence of two main sources of overflow water: one approaching the sill in the East Greenland Current and the other via the North Icelandic Jet. Using an objective technique based on the hydrographic properties of the water, the transports of these two sources are found to be 2.54 ± 0.17 Sv and 1.00 ± 0.17 Sv, respectively. We further partition the East Greenland Current source into that carried by the shelfbreak jet (1.50 ± 0.16 Sv) versus that transported by a separated branch of the current on the Iceland slope (1.04 ± 0.15 Sv). Over the course of the year the total overflow transport is more consistent than the transport in either branch; compensation takes place among the pathways that maintains a stable total overflow transport. This is especially true for the two East Greenland Current branches whose transports vary out of phase with each other on weekly and longer time scales. We argue that wind forcing plays a role in this partitioning.The mooring and analysis work was supported by NSF OCE research grants OCE-0959381 and OCE-1433958, by the European Union 7th Framework Programme (FP7 2007-2013) under grant agreement n. 308299 NACLIM, and and by the Research Council of Norway through the Fram Centre Flaggship project 6606-299.2017-03-2

Upstream sources of the Denmark Strait Overflow : observations from a high-resolution mooring array

© The Author(s), 2016. This is the author's version of the work and is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Deep Sea Research Part I: Oceanographic Research Papers 112 (2016): 94-112, doi:10.1016/j.dsr.2016.02.007.We present the first results from a densely instrumented mooring array upstream of the Denmark Strait sill, extending from the Iceland shelfbreak to the Greenland shelf. The array was deployed from September 2011 to July 2012, and captured the vast majority of overflow water denser than 27.8 kgm-3 approaching the sill. The mean transport of overflow water over the length of the deployment was 3.54 ± 0.16 Sv. Of this, 0.58 Sv originated from below sill depth, revealing that aspiration takes place in Denmark Strait. We confirm the presence of two main sources of overflow water: one approaching the sill in the East Greenland Current and the other via the North Icelandic Jet. Using an objective technique based on the hydrographic properties of the water, the transports of these two sources are found to be 2.54 ± 0.17 Sv and 1.00 ± 0.17 Sv, respectively. We further partition the East Greenland Current source into that carried by the shelfbreak jet (1.50 ± 0.16 Sv) versus that transported by a separated branch of the current on the Iceland slope (1.04 ± 0.15 Sv). Over the course of the year the total overflow transport is more consistent than the transport in either branch; compensation takes place among the pathways that maintains a stable total overflow transport. This is especially true for the two East Greenland Current branches whose transports vary out of phase with each other on weekly and longer time scales. We argue that wind forcing plays a role in this partitioning.The mooring and analysis work was supported by NSF OCE research grants OCE-0959381 and OCE-1433958, by the European Union 7th Framework Programme (FP7 2007-2013) under grant agreement n. 308299 NACLIM, and and by the Research Council of Norway through the Fram Centre Flaggship project 6606-299.2017-03-2

Investigating the genetic architecture of noncognitive skills using GWAS-by-subtraction

Little is known about the genetic architecture of traits affecting educational attainment other than cognitive ability. We used genomic structural equation modeling and prior genome-wide association studies (GWASs) of educational attainment (n = 1,131,881) and cognitive test performance (n = 257,841) to estimate SNP associations with educational attainment variation that is independent of cognitive ability. We identified 157 genome-wide-significant loci and a polygenic architecture accounting for 57% of genetic variance in educational attainment. Noncognitive genetics were enriched in the same brain tissues and cell types as cognitive performance, but showed different associations with gray-matter brain volumes. Noncognitive genetics were further distinguished by associations with personality traits, less risky behavior and increased risk for certain psychiatric disorders. For socioeconomic success and longevity, noncognitive and cognitive-performance genetics demonstrated associations of similar magnitude. By conducting a GWAS of a phenotype that was not directly measured, we offer a view of genetic architecture of noncognitive skills influencing educational success

Investigating the genetic architecture of noncognitive skills using GWAS-by-subtraction

Little is known about the genetic architecture of traits affecting educational attainment other than cognitive ability. We used genomic structural equation modeling and prior genome-wide association studies (GWASs) of educational attainment (n = 1,131,881) and cognitive test performance (n = 257,841) to estimate SNP associations with educational attainment variation that is independent of cognitive ability. We identified 157 genome-wide-significant loci and a polygenic architecture accounting for 57% of genetic variance in educational attainment. Noncognitive genetics were enriched in the same brain tissues and cell types as cognitive performance, but showed different associations with gray-matter brain volumes. Noncognitive genetics were further distinguished by associations with personality traits, less risky behavior and increased risk for certain psychiatric disorders. For socioeconomic success and longevity, noncognitive and cognitive-performance genetics demonstrated associations of similar magnitude. By conducting a GWAS of a phenotype that was not directly measured, we offer a view of genetic architecture of noncognitive skills influencing educational success