An official website of the United States government
Regional and intra-annual stability of dissolved organic matter composition and biolability in high-latitude Alaskan rivers: DOM in high-latitude rivers
- Award ID(s):
- 1636476
- PAR ID:
- 10085403
- Date Published:
- Journal Name:
- Limnology and Oceanography
- Volume:
- 63
- Issue:
- 4
- ISSN:
- 0024-3590
- Page Range / eLocation ID:
- 1605 to 1621
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
Abstract How individual organisms adapt to nonoptimal conditions through physiological acclimatization is central to predicting the consequences of unusual abiotic and biotic conditions such as those produced by marine heat waves. The Northeast Pacific, including the Gulf of Alaska, experienced an extreme warming event (2014–2016, “The Blob”) that affected all trophic levels and led to large‐scale changes in the community. The marine copepodNeocalanus flemingeriis a key member of the subarctic Pacific pelagic ecosystem. During the spring phytoplankton bloom this copepod builds substantial lipid stores as it prepares for its nonfeeding adult phase. A 3‐year comparison of gene expression profiles of copepods collected in Prince William Sound in the Gulf of Alaska between 2015 and 2017 included two high‐temperature years (2015 and 2016) and one year with very low phytoplankton abundances (2016). The largest differences in gene expression were between high and low chlorophyll years, and not between warm and cool years. The observed gene expression patterns were indicative of physiological acclimatization. The predominant signal in 2016 was the down‐regulation of genes involved in glycolysis and its incoming pathways, consistent with the modulation of metabolic rates in response to prolonged low food conditions. Despite the down‐regulation of genes involved in metabolism, there was no evidence of suppression of protein synthesis based on gene expression or behavioural activity. Genes involved in muscle function were up‐regulated, and the copepods were actively swimming and responsive to stimuli at collection. However, genes involved in fatty acid metabolism were down‐regulated in 2016, suggesting reduced lipid accumulation.more » « less
-
Abstract This work investigates mesoscale structures in the northern high‐latitude thermosphere using an ascending‐descending accelerometry (ADA) technique to determine whether observed in‐track acceleration perturbations are influenced by in‐track winds. The ADA technique is applied to accelerometer measurements from the Challenging Minisatellite Payload mission between 2003 and 2006 during quiet geomagnetic activity, revealing a climatological view of regularly occurring acceleration perturbation structures. The ADA technique reveals a structured acceleration enhancement on the dayside with a strong signature of density dominance confined to a spatial envelope ranging from 8:00 to 17:00 magnetic local time (MLT) and between 72° and 82° magnetic latitude, aligning with past observations of the cusp density enhancement. Additionally, this sector displays a wind perturbation structure with a reversal in direction that coincides with the center of the enhancement. The premidnight quadrant shows strong evidence of wind influence in the acceleration perturbations from 18:00 to 24:00 MLT between 70° and 90° magnetic latitude associated with southward wind perturbations. This suggests that past analyses of this region could have misidentified this structure as a density enhancement by neglecting in‐track wind influences in accelerometry‐derived mass density data sets. The early morning quadrant consists of negative acceleration perturbations attributed to density depletions, with signatures of southward wind perturbations. These mass density perturbations, in conjunction with in‐track wind perturbations, suggest that the coupled ionosphere‐thermosphere mechanisms responsible for the high‐latitude density structure also influence the wind structure. This work is supplemented with TIEGCM simulations to verify the accuracy of ADA and highlight discrepancies between the simulations and observations.more » « less
-
SUMMARY Recent geomagnetic observations reveal localized oscillations in the field’s secular acceleration at high latitudes, with periods of about 20 yr. Several types of waves in rotating magnetized fluids have been proposed to explain equatorial oscillations with similar high frequencies. Among these are non-axisymmetric Alfvén waves, magneto-Coriolis waves and, in the presence of fluid stratification, magnetic-Archimedes–Coriolis (MAC) waves. We explore the hypothesis that the observed high latitude patterns are the signature of MAC waves by modelling their generation in Earth’s core. We quantitatively assess several generation mechanisms using output from dynamo simulations in a theoretical framework due to Lighthill. While the spatio-temporal structure of the sources from the dynamo simulations are expected to be realistic, their amplitudes are extrapolated to reflect differences between the simulation’s parameter space and Earth-like conditions. We estimate full wave spectra spanning monthly to centennial frequencies for three plausible excitation sources: thermal fluctuations, Lorentz force and magnetic induction. When focusing on decadal frequencies, the Lorentz force appears to be most effective in generating high-latitude MAC waves with amplitude estimates falling within an order of magnitude of observed oscillations. Overall, this study puts forward MAC waves as a viable explanation, in the presence of fluid stratification at the top of Earth’s core, for observed field variations at high latitudes.more » « less
-
Abstract Ecosystems at high latitudes are changing rapidly in response to climate change. To understand changes in carbon fluxes across seasonal to multi‐decadal timescales, long‐term in situ measurements from eddy covariance networks are needed. However, there are large spatiotemporal gaps in the high‐latitude eddy covariance network. Here we used the relative extrapolation error index in machine learning‐based upscaled gross primary production as a measure of network representativeness and as the basis for a network optimization. We show that the relative extrapolation error index has steadily decreased from 2001 to 2020, suggesting diminishing upscaling errors. In experiments where we limit site activity by either setting a maximum duration or by ending measurements at a fixed time those errors increase significantly, in some cases setting the network status back more than a decade. Our experiments also show that with equal site activity across different theoretical network setups, a more spread out design with shorter‐term measurements functions better in terms of larger‐scale representativeness than a network with fewer long‐term towers. We developed a method to select optimized site additions for a network extension, which blends an objective modeling approach with expert knowledge. This method greatly outperforms an unguided network extension and can compensate for suboptimal human choices. For the Canadian Arctic we show several optimization scenarios and find that especially the Canadian high Arctic and north east tundra benefit greatly from addition sites. Overall, it is important to keep sites active and where possible make the extra investment to survey new strategic locations.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1002/lno.10795
