FROM THE GUEST EDITORS. Introduction to the Special Issue on Ocean-Ice Interaction

The end of 2016 is an uneasy moment for climate science in the United States. With a new Administration and a new Congress arriving in January 2017, future support for climate science and observing systems is uncertain. Against this backdrop, this special issue of Oceanographyon ocean-ice interaction is timely. Although it was not our intent to highlight climate change, the fragile nature of Earth’s cryosphere and how it is responding to a warming world are essential parts of each article. Many aspects of the shrinking cryosphere are not yet understood, but the research described in these pages points to larger-than-anticipated—and alarming—changes to the planet’s large ice sheets, with associated future increases in global sea levels. Importantly, the articles in this special issue demonstrate the value to society of continuing vigorous scientific research that will enable us to better understand our planet’s rapidly changing polar environments

Bathymetry of Southeast Greenland From Oceans Melting Greenland (OMG) Data

Southeast Greenland has been a major participant in the ice sheet mass loss over the last several decades. Interpreting the evolution of glacier fronts requires information about their depth below sea level and ocean thermal forcing, which are incompletely known in the region. Here, we combine airborne gravity and multibeam echo sounding data from the National Aeronautics and Space Administration's Oceans Melting Greenland (OMG) mission with ocean probe and fishing boat depth data to reconstruct the bathymetry extending from the glacier margins to the edges of the continental shelf. We perform a three‐dimensional inversion of the gravity data over water and merge the solution with a mass conservation reconstruction of bed topography over land. In contrast with other parts of Greenland, we find few deep troughs connecting the glaciers to the sources of warm Atlantic Water, amidst a relatively uniform, shallow (350 m) continental shelf. The deep channels include the Kangerlugssuaq, Sermilik, Gyldenløve, and Tingmiarmiut Troughs

Oceans Melting Greenland: Early Results from NASA's Ocean-Ice Mission in Greenland

Melting of the Greenland Ice Sheet represents a major uncertainty in projecting future rates of global sea level rise. Much of this uncertainty is related to a lack of knowledge about subsurface ocean hydrographic properties, particularly heat content, how these properties are modified across the continental shelf, and about the extent to which the ocean interacts with glaciers. Early results from NASA’s five-year Oceans Melting Greenland (OMG) mission, based on extensive hydrographic and bathymetric surveys, suggest that many glaciers terminate in deep water and are hence vulnerable to increased melting due to ocean-ice interaction. OMG will track ocean conditions and ice loss at glaciers around Greenland through the year 2020, providing critical information about ocean-driven Greenland ice mass loss in a warming climate

Comprehensive molecular characterization of gastric adenocarcinoma

Gastric cancer is a leading cause of cancer deaths, but analysis of its molecular and clinical characteristics has been complicated by histological and aetiological heterogeneity. Here we describe a comprehensive molecular evaluation of 295 primary gastric adenocarcinomas as part of The Cancer Genome Atlas (TCGA) project. We propose a molecular classification dividing gastric cancer into four subtypes: tumours positive for Epstein–Barr virus, which display recurrent PIK3CA mutations, extreme DNA hypermethylation, and amplification of JAK2, CD274 (also known as PD-L1) and PDCD1LG2 (also knownasPD-L2); microsatellite unstable tumours, which show elevated mutation rates, including mutations of genes encoding targetable oncogenic signalling proteins; genomically stable tumours, which are enriched for the diffuse histological variant and mutations of RHOA or fusions involving RHO-family GTPase-activating proteins; and tumours with chromosomal instability, which show marked aneuploidy and focal amplification of receptor tyrosine kinases. Identification of these subtypes provides a roadmap for patient stratification and trials of targeted therapies

Altimetry for the future: Building on 25 years of progress

In 2018 we celebrated 25 years of development of radar altimetry, and the progress achieved by this methodology in the fields of global and coastal oceanography, hydrology, geodesy and cryospheric sciences. Many symbolic major events have celebrated these developments, e.g., in Venice, Italy, the 15th (2006) and 20th (2012) years of progress and more recently, in 2018, in Ponta Delgada, Portugal, 25 Years of Progress in Radar Altimetry. On this latter occasion it was decided to collect contributions of scientists, engineers and managers involved in the worldwide altimetry community to depict the state of altimetry and propose recommendations for the altimetry of the future. This paper summarizes contributions and recommendations that were collected and provides guidance for future mission design, research activities, and sustainable operational radar altimetry data exploitation. Recommendations provided are fundamental for optimizing further scientific and operational advances of oceanographic observations by altimetry, including requirements for spatial and temporal resolution of altimetric measurements, their accuracy and continuity. There are also new challenges and new openings mentioned in the paper that are particularly crucial for observations at higher latitudes, for coastal oceanography, for cryospheric studies and for hydrology. The paper starts with a general introduction followed by a section on Earth System Science including Ocean Dynamics, Sea Level, the Coastal Ocean, Hydrology, the Cryosphere and Polar Oceans and the ‘‘Green” Ocean, extending the frontier from biogeochemistry to marine ecology. Applications are described in a subsequent section, which covers Operational Oceanography, Weather, Hurricane Wave and Wind Forecasting, Climate projection. Instruments’ development and satellite missions’ evolutions are described in a fourth section. A fifth section covers the key observations that altimeters provide and their potential complements, from other Earth observation measurements to in situ data. Section 6 identifies the data and methods and provides some accuracy and resolution requirements for the wet tropospheric correction, the orbit and other geodetic requirements, the Mean Sea Surface, Geoid and Mean Dynamic Topography, Calibration and Validation, data accuracy, data access and handling (including the DUACS system). Section 7 brings a transversal view on scales, integration, artificial intelligence, and capacity building (education and training). Section 8 reviews the programmatic issues followed by a conclusion

Global Oceans, BAMS State of the Climate in 2021, Chapter 3

Patterns of variability in ocean properties are often closely related to large-scale climate pattern indices, and 2021 is no exception. The year 2021 started and ended with La Niña conditions, charmingly dubbed a “double-dip” La Niña. Hence, stronger-than-normal easterly trade winds in the tropical south Pacific drove westward surface current anomalies in the equatorial Pacific; reduced sea surface temperature (SST) and upper ocean heat content in the eastern tropical Pacific; increased sea level, upper ocean heat content, and salinity in the western tropical Pacific; resulted in a rim of anomalously high chlorophyll-a (Chla) on the poleward and westward edges of the anomalously cold SST wedge in the eastern equatorial Pacific; and increased precipitation over the Maritime Continent. The Pacific decadal oscillation remained strongly in a negative phase in 2021, with negative SST and upper ocean heat content anomalies around the eastern and equatorial edges of the North Pacific and positive anomalies in the center associated with low Chla anomalies. The South Pacific exhibited similar patterns. Fresh anomalies in the northeastern Pacific shifted towards the west coast of North America. The Indian Ocean dipole (IOD) was weakly negative in 2021, with small positive SST anomalies in the east and nearly-average anomalies in the west. Nonetheless, upper ocean heat content was anomalously high in the west and lower in the east, with anomalously high freshwater flux and low sea surface salinities (SSS) in the east, and the opposite pattern in the west, as might be expected during a negative phase of that climate index. In the Atlantic, the only substantial cold anomaly in SST and upper ocean heat content persisted east of Greenland in 2021, where SSS was also low, all despite the weak winds and strong surface heat flux anomalies into the ocean expected during a negative phase of the North Atlantic Oscillation. These anomalies held throughout much of 2021. An Atlantic and Benguela Niño were both evident, with above-average SST anomalies in the eastern equatorial Atlantic and the west coast of southern Africa. Over much of the rest of the Atlantic, SSTs, upper ocean heat content, and sea level anomalies were above average. Anthropogenic climate change involves long-term trends, as this year’s chapter sidebars emphasize. The sidebars relate some of the latest IPCC ocean-related assessments (including carbon, the section on which is taking a hiatus from our report this year). This chapter estimates that SST increased at a rate of 0.16–0.19°C decade−1 from 2000 to 2021, 0–2000-m ocean heat content warmed by 0.57–0.73 W m−2 (applied over Earth’s surface area) from 1993 to 2021, and global mean sea level increased at a rate of 3.4 ± 0.4 mm yr−1 from 1993 to 2021. Global mean SST, which is more subject to interannual variations than ocean heat content and sea level, with values typically reduced during La Niña, was ~0.1°C lower in 2021 than in 2020. However, from 2020 to 2021, annual average ocean heat content from 0 to 2000 dbar increased at a rate of ~0.95 W m−2, and global sea level increased by ~4.9 mm. Both were the highest on record in 2021, and with year-on-year increases substantially exceeding their trend rates of recent decades

Altimetry for the future: building on 25 years of progress

In 2018 we celebrated 25 years of development of radar altimetry, and the progress achieved by this methodology in the fields of global and coastal oceanography, hydrology, geodesy and cryospheric sciences. Many symbolic major events have celebrated these developments, e.g., in Venice, Italy, the 15th (2006) and 20th (2012) years of progress and more recently, in 2018, in Ponta Delgada, Portugal, 25 Years of Progress in Radar Altimetry. On this latter occasion it was decided to collect contributions of scientists, engineers and managers involved in the worldwide altimetry community to depict the state of altimetry and propose recommendations for the altimetry of the future. This paper summarizes contributions and recommendations that were collected and provides guidance for future mission design, research activities, and sustainable operational radar altimetry data exploitation. Recommendations provided are fundamental for optimizing further scientific and operational advances of oceanographic observations by altimetry, including requirements for spatial and temporal resolution of altimetric measurements, their accuracy and continuity. There are also new challenges and new openings mentioned in the paper that are particularly crucial for observations at higher latitudes, for coastal oceanography, for cryospheric studies and for hydrology. The paper starts with a general introduction followed by a section on Earth System Science including Ocean Dynamics, Sea Level, the Coastal Ocean, Hydrology, the Cryosphere and Polar Oceans and the “Green” Ocean, extending the frontier from biogeochemistry to marine ecology. Applications are described in a subsequent section, which covers Operational Oceanography, Weather, Hurricane Wave and Wind Forecasting, Climate projection. Instruments’ development and satellite missions’ evolutions are described in a fourth section. A fifth section covers the key observations that altimeters provide and their potential complements, from other Earth observation measurements to in situ data. Section 6 identifies the data and methods and provides some accuracy and resolution requirements for the wet tropospheric correction, the orbit and other geodetic requirements, the Mean Sea Surface, Geoid and Mean Dynamic Topography, Calibration and Validation, data accuracy, data access and handling (including the DUACS system). Section 7 brings a transversal view on scales, integration, artificial intelligence, and capacity building (education and training). Section 8 reviews the programmatic issues followed by a conclusion

A Global Evaluation of Ocean Bottom Pressure from GRACE, OMCT, and Steric-Corrected Altimetry

Ocean bottom pressure (OBP) from the Gravity Recovery and Climate Experiment (GRACE) and the Ocean Model for Circulation and Tides (OMCT) are compared globally with OBP computed from altimetry corrected for steric variations from Argo floats from January 2005 to December 2007. Two methods of smoothing the GRACE data are examined. The first uses a standard Gaussian smoother with a radius of 300 km. The second method projects those smoothed maps onto empirical orthogonal functions derived from OMCT in a least squares estimation in order to produce maps that better agree with the physical processes embodied by the model. These new maps agree significantly better with estimates from the steric-corrected altimetry, reducing the variance on average by 30% over 70% of the ocean. This is compared to smaller reductions over only 14% of the ocean using the 300-km Gaussian maps and 56% of the ocean using OMCT maps. The OMCT maps do not reduce variance as much in the Southern Ocean where OBP variations are largest, whereas the GRACE maps do. Based on this analysis, it is estimated that the local, or point-to-point, uncertainty of new EOF filtered maps of GRACE OBP is 1.3 (one standard deviation)

Analysis of Large-scale Ocean Bottom Pressure Variability in the North Pacific

[1] We use the leading empirical orthogonal functions (EOFs) of ocean bottom pressure (OBP) derived from an ocean model and the technique of EOF reconstruction to reduce noise in the large-scale OBP variations derived from the Gravity Recovery and Climate Experiment (GRACE). The subsequent OBP variations from the model and GRACE are then examined in the North Pacific between January 2003 and May 2007. Although annual and semiannual variations are similar, GRACE observes large interannual fluctuations poleward of 30°, where OBP increases from a low of nearly 3 cm below normal in early 2003 to normal throughout 2004 and 2005, then an increase of nearly the same magnitude in 2006. These fluctuations have also been observed in OBP inferred from satellite altimetry corrected for steric variations computed from Argo float data. Since GRACE and steric-corrected altimetry are completely independent observations of OBP, we conclude that the model has errors or deficiencies in predicting the interannual OBP fluctuations in the North Pacific