Description: © The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Gehrels, W. R., Dangendorf, S., Barlow, N. L. M., Saher, M. H., Long, A. J., Woodworth, P. L., Piecuch, C. G., & Berk, K. A preindustrial sea-level rise hotspot along the Atlantic Coast of North America. Geophysical Research Letters, 47(4), (2020): e2019GL085814, doi:10.1029/2019GL085814.

Description: The Atlantic coast of North America north of Cape Hatteras has been proposed as a “hotspot” of late 20th century sea‐level rise. Here we test, using salt‐marsh proxy sea‐level records, if this coast experienced enhanced sea‐level rise over earlier multidecadal‐centennial periods. While we find in agreement with previous studies that 20th century rates of sea‐level change were higher compared to rates during preceding centuries, rates of 18th century sea‐level rise were only slightly lower, suggesting that the “hotspot” is a reoccurring feature for at least three centuries. Proxy sea‐level records from North America (Iceland) are negatively (positively) correlated with centennial changes in the North Atlantic Oscillation. They are consistent with sea‐level “fingerprints” of Arctic ice melt, and we therefore hypothesize that sea‐level fluctuations are related to changes in Arctic land‐ice mass. Predictions of future sea‐level rise should take into account these long‐term fluctuating rates of natural sea‐level change.

Description: This work is funded by the Natural Environment Research Council (grant NE/G003440/1). All radiocarbon dating was supported by the Natural Environment Research Council Radiocarbon Facility (allocations 1490.0810, 1566.0511, 1604.0112). Mark Wood assisted with fieldwork. Rob Scaife analyzed pollen data for core SN‐3.3. Sönke Dangendorf and Kevin Berk acknowledge the University of Siegen for their support within the PEPSEA project. Christopher Piecuch was supported by National Science Foundation awards OCE‐1558966 and OCE‐1834739. We thank project members Miguel Ángel Morales Maqueda, Chris Hughes, Vassil Roussenov and Ric Williams for valuable discussions. We are grateful to the International Space Science Institute (ISSI; Bern, Switzerland) for support of the International Team “Towards a unified Sea Level Record”. Data used in this paper are freely available online (https://www.doi.org/10/dgvq).

Description: The Global Sea-level Observing System (GLOSS) was established by the Intergovernmental Oceanographic Commission (IOC) of the United Nations Educational, Scientific and Cultural Organization (UNESCO) in 1985 to provide oversight and coordination for global and regional sea-level networks in support of scien- tific research. The first GLOSS Implementation Plan (GIP) in 1990 established the GLOSS Core Network (GCN) of ~300 tide gauges distributed around the world, technical standards for GLOSS tide gauge stations, as well as the basic terms and obligations for Member States participating in GLOSS. The second GIP in 1997 expanded the GLOSS programme to include sub-networks focused on long historical records suitable for the detection of long-term sea- level trends and accelerations (GLOSS-LTT), a cali- bration network for satellite altimetry (GLOSS-ALT), and a network suitable for monitoring aspects of the global ocean circulation (GLOSS-OC). In addition, a strategy for integrating Global Positioning System (GPS) into monitoring of land levels at GLOSS tide gauges was developed. The focus of the GIP 2012 remains the GCN and the datasets that result from this network. The new plan calls for two significant upgrades to the GCN moti- vated by scientific and operational requirements: 1) all GCN stations are required to report data in near-real time, which will be tracked at a Sea-level Station Monitoring Facility. This will involve upgrades in power, data acquisition plat- forms, and communication packages; however, these upgrades are cost-effective in terms of the benefits that a real-time system will provide for ocean monitoring and improved station perfor- mance due to early detection of station malfunc- tions; 2) continuous measurements of the Global Navigation Satellite System (GNSS), in particular the U.S. Global Positioning System (GPS), the Russian GLONASS, or the newly established European GALILEO, or equivalent systems, in the vicinity of the tide gauge benchmark (TGBM) are required for all GCN stations. This upgrade will support satellite altimetry calibration and research efforts aimed at determining geocentric global sea-level rise rates as well as regional changes in sea level. Most relevant, vertical land movements can signifi- cantly alter the rates of sea-level rise expected from the sole climatic contributions of ocean ther- mal expansion and land-based ice melting, possi- bly magnifying the impacts of sea-level rise on the coast. In many cases, this requirement can be met by taking advantage of existing GNSS receivers maintained by other groups, as long as a precise geodetic tie to the GCN tide gauge can be made using, e.g. conventional levelling. The organization of the plan is as follows. An over- view of the GLOSS programme (chapter 1) and a brief summary of the uses of tide gauge data (chapter 2) are presented. The current status of the GLOSS programme is considered (chapter 3), followed by a discussion of the sea-level monitoring requirements raised by advisory groups and panels (chapter 4), as well as a self-assessment based on specific research and operational applications (chapter 5). These requirements are used to develop implementation goals for the GLOSS networks and data centres (chapter 6). Minor modifications are proposed for the administrative structure of GLOSS aimed at providing improved oversight of the imple- mentation plan (chapter 7). The success of the plan depends critically on the participation of Member States, whose obligations are summarized (chapter 8). The successful Training, Education and Mutual Assistance programmes that have been a corner stone of GLOSS will be continued to help meet implementation requirements (chapter 9). Additional technical and programmatic details are included in a set of appendices.

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Description: © The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Ponte, R. M., Carson, M., Cirano, M., Domingues, C. M., Jevrejeva, S., Marcos, M., Mitchum, G., van de Wal, R. S. W., Woodworth, P. L., Ablain, M., Ardhuin, F., Ballu, V., Becker, M., Benveniste, J., Birol, F., Bradshaw, E., Cazenave, A., De Mey-Fremaux, P., Durand, F., Ezer, T., Fu, L., Fukumori, I., Gordon, K., Gravelle, M., Griffies, S. M., Han, W., Hibbert, A., Hughes, C. W., Idier, D., Kourafalou, V. H., Little, C. M., Matthews, A., Melet, A., Merrifield, M., Meyssignac, B., Minobe, S., Penduff, T., Picot, N., Piecuch, C., Ray, R. D., Rickards, L., Santamaria-Gomez, A., Stammer, D., Staneva, J., Testut, L., Thompson, K., Thompson, P., Vignudelli, S., Williams, J., Williams, S. D. P., Woppelmann, G., Zanna, L., & Zhang, X. Towards comprehensive observing and modeling systems for monitoring and predicting regional to coastal sea level. Frontiers in Marine Science, 6, (2019): 437, doi:10.3389/fmars.2019.00437.

Description: A major challenge for managing impacts and implementing effective mitigation measures and adaptation strategies for coastal zones affected by future sea level (SL) rise is our limited capacity to predict SL change at the coast on relevant spatial and temporal scales. Predicting coastal SL requires the ability to monitor and simulate a multitude of physical processes affecting SL, from local effects of wind waves and river runoff to remote influences of the large-scale ocean circulation on the coast. Here we assess our current understanding of the causes of coastal SL variability on monthly to multi-decadal timescales, including geodetic, oceanographic and atmospheric aspects of the problem, and review available observing systems informing on coastal SL. We also review the ability of existing models and data assimilation systems to estimate coastal SL variations and of atmosphere-ocean global coupled models and related regional downscaling efforts to project future SL changes. We discuss (1) observational gaps and uncertainties, and priorities for the development of an optimal and integrated coastal SL observing system, (2) strategies for advancing model capabilities in forecasting short-term processes and projecting long-term changes affecting coastal SL, and (3) possible future developments of sea level services enabling better connection of scientists and user communities and facilitating assessment and decision making for adaptation to future coastal SL change.

Description: RP was funded by NASA grant NNH16CT00C. CD was supported by the Australian Research Council (FT130101532 and DP 160103130), the Scientific Committee on Oceanic Research (SCOR) Working Group 148, funded by national SCOR committees and a grant to SCOR from the U.S. National Science Foundation (Grant OCE-1546580), and the Intergovernmental Oceanographic Commission of UNESCO/International Oceanographic Data and Information Exchange (IOC/IODE) IQuOD Steering Group. SJ was supported by the Natural Environmental Research Council under Grant Agreement No. NE/P01517/1 and by the EPSRC NEWTON Fund Sustainable Deltas Programme, Grant Number EP/R024537/1. RvdW received funding from NWO, Grant 866.13.001. WH was supported by NASA (NNX17AI63G and NNX17AH25G). CL was supported by NASA Grant NNH16CT01C. This work is a contribution to the PIRATE project funded by CNES (to TP). PT was supported by the NOAA Research Global Ocean Monitoring and Observing Program through its sponsorship of UHSLC (NA16NMF4320058). JS was supported by EU contract 730030 (call H2020-EO-2016, “CEASELESS”). JW was supported by EU Horizon 2020 Grant 633211, Atlantos.