Recent Changes in Central and Eastern Pacific El Niño

Recent research indicates that characteristics of El Niño and the Southern Oscillation (ENSO) have changed over the past several decades. Here, I examined different flavors of El Niño in the observational record and the recent changes in the character of El Niño events. The fundamental physical processes that drive ENSO were described and the Eastern Pacific (EP) and Central Pacific (CP) types or flavors of El Niño were defined. Using metrics from the peer-reviewed literature, I examined several historical data sets to interpret El Niño behavior from 1950-2010. A Monte Carlo Simulation was then applied to output from coupled model simulations to test the statistical significance of recent observations surrounding EP and CP El Niño. Results suggested that EP and CP El Niño had been occurring in a similar fashion over the past 60 years with natural variability, but no significant increase in CP El Niño behavior

The Ice Shelf of Petermann Gletscher, North Greenland, and Its Connection to the Arctic and Atlantic Oceans

Petermann Gletscher in North Greenland features the second largest floating ice shelf in the Northern Hemisphere. This paper describes the history of its exploration and presents new ocean and glacier observations. We find that the floating ice shelf is strongly coupled to the ocean below and to Nares Strait at time scales from tidal to interannual. Our observations cover the 2012 to 2016 period after two large calving events took place in 2010 and 2012 that reduced the ice shelf area by 380 km2 to about 870 km2 today. A potential third breakup, of an additional 150 km2, is anticipated by a large fracture that extends from the margin to the center of the glacier

Tidal modulation of buoyant flow and basal melt beneath Petermann Gletscher Ice Shelf, Greenland.

A set of collocated, in situ oceanographic and glaciological measurements from Petermann Gletscher Ice Shelf, Greenland, provides insights into the dynamics of under‐ice flow driving basal melting. At a site 16 km seaward of the grounding line within a longitudinal basal channel, two conductivity‐temperature (CT) sensors beneath the ice base and a phase‐sensitive radar on the ice surface were used to monitor the coupled ice shelf‐ocean system. A six month time series spanning August 23, 2015 to February 12, 2016 exhibited two distinct periods of ice‐ocean interactions. Between August and December, radar‐derived basal melt rates featured fortnightly peaks of ~15 m yr‐1 which preceded the arrival of cold and fresh pulses in the ocean that had high concentrations of subglacial runoff and glacial meltwater. Estimated current speeds reached 0.20‐0.40 m s‐1 during these pulses, consistent with a strengthened meltwater plume from freshwater enrichment. Such signals did not occur between December and February, when ice‐ocean interactions instead varied at principal diurnal and semidiurnal tidal frequencies, and lower melt rates and current speeds prevailed. A combination of estimated current speeds and meltwater concentrations from the two CT sensors yields estimates of subglacial runoff and glacial meltwater volume fluxes that vary between 10 and 80 m3 s‐1 during the ocean pulses. Area‐average upstream ice shelf melt rates from these fluxes are up to 170 m yr‐1, revealing that these strengthened plumes had already driven their most intense melting before arriving at the study site

Summer surface melt thins Petermann Gletscher Ice Shelf by enhancing channelized basal melt

Increasing ocean and air temperatures have contributed to the removal of floating ice shelves from several Greenland outlet glaciers; however, the specific contribution of these external forcings remains poorly understood. Here we use atmospheric, oceanographic and glaciological time series data from the ice shelf of Petermann Gletscher, NW Greenland to quantify the forcing of the ocean and atmosphere on the ice shelf at a site ~16 km from the grounding line within a large sub-ice-shelf channel. Basal melt rates here indicate a strong seasonality, rising from a winter mean of 2 m a−1 to a maximum of 80 m a−1 during the summer melt season. This increase in basal melt rates confirms the direct link between summer atmospheric warming around Greenland and enhanced ocean-forced melting of its remaining ice shelves. We attribute this enhanced melting to increased discharge of subglacial runoff into the ocean at the grounding line, which strengthens under-ice currents and drives a greater ocean heat flux toward the ice base

Suppressed basal melting in the eastern Thwaites Glacier grounding zone

This work is from the MELT project, a component of the International Thwaites Glacier Collaboration (ITGC). Support from the National Science Foundation (NSF, grant no. 1739003) and the Natural Environment Research Council (NERC, grant no. NE/S006656/1). Logistics provided by NSF U.S. Antarctic Program and NERC British Antarctic Survey. The ship-based CTD data were supported by the ITGC TARSAN project (NERC grant nos. NE/S006419/1 and NE/S006591/1; NSF grant no. 1929991). ITGC contribution no. ITGC 047.Thwaites Glacier is one of the fastest-changing ice–ocean systems in Antarctica1,2,3. Much of the ice sheet within the catchment of Thwaites Glacier is grounded below sea level on bedrock that deepens inland4, making it susceptible to rapid and irreversible ice loss that could raise the global sea level by more than half a metre2,3,5. The rate and extent of ice loss, and whether it proceeds irreversibly, are set by the ocean conditions and basal melting within the grounding-zone region where Thwaites Glacier first goes afloat3,6, both of which are largely unknown. Here we show—using observations from a hot-water-drilled access hole—that the grounding zone of Thwaites Eastern Ice Shelf (TEIS) is characterized by a warm and highly stable water column with temperatures substantially higher than the in situ freezing point. Despite these warm conditions, low current speeds and strong density stratification in the ice–ocean boundary layer actively restrict the vertical mixing of heat towards the ice base7,8, resulting in strongly suppressed basal melting. Our results demonstrate that the canonical model of ice-shelf basal melting used to generate sea-level projections cannot reproduce observed melt rates beneath this critically important glacier, and that rapid and possibly unstable grounding-line retreat may be associated with relatively modest basal melt rates.Publisher PDFPeer reviewe

Suppressed basal melting in the eastern Thwaites Glacier grounding zone

Thwaites Glacier is one of the fastest-changing ice–ocean systems in Antarctica1,2,3. Much of the ice sheet within the catchment of Thwaites Glacier is grounded below sea level on bedrock that deepens inland4, making it susceptible to rapid and irreversible ice loss that could raise the global sea level by more than half a metre2,3,5. The rate and extent of ice loss, and whether it proceeds irreversibly, are set by the ocean conditions and basal melting within the grounding-zone region where Thwaites Glacier first goes afloat3,6, both of which are largely unknown. Here we show—using observations from a hot-water-drilled access hole—that the grounding zone of Thwaites Eastern Ice Shelf (TEIS) is characterized by a warm and highly stable water column with temperatures substantially higher than the in situ freezing point. Despite these warm conditions, low current speeds and strong density stratification in the ice–ocean boundary layer actively restrict the vertical mixing of heat towards the ice base7,8, resulting in strongly suppressed basal melting. Our results demonstrate that the canonical model of ice-shelf basal melting used to generate sea-level projections cannot reproduce observed melt rates beneath this critically important glacier, and that rapid and possibly unstable grounding-line retreat may be associated with relatively modest basal melt rates

Swirls and scoops: Ice base melt revealed by multibeam imagery of an Antarctic ice shelf

Knowledge gaps about how the ocean melts Antarctica’s ice shelves, borne from a lack of observations, lead to large uncertainties in sea level predictions. Using high-resolution maps of the underside of Dotson Ice Shelf, West Antarctica, we reveal the imprint that ice shelf basal melting leaves on the ice. Convection and intermittent warm water intrusions form widespread terraced features through slow melting in quiescent areas, while shear-driven turbulence rapidly melts smooth, eroded topographies in outflow areas, as well as enigmatic teardrop-shaped indentations that result from boundary-layer flow rotation. Full-thickness ice fractures, with bases modified by basal melting and convective processes, are observed throughout the area. This new wealth of processes, all active under a single ice shelf, must be considered to accurately predict future Antarctic ice shelf melt

Antiinflammatory Therapy with Canakinumab for Atherosclerotic Disease

Background: Experimental and clinical data suggest that reducing inflammation without affecting lipid levels may reduce the risk of cardiovascular disease. Yet, the inflammatory hypothesis of atherothrombosis has remained unproved. Methods: We conducted a randomized, double-blind trial of canakinumab, a therapeutic monoclonal antibody targeting interleukin-1β, involving 10,061 patients with previous myocardial infarction and a high-sensitivity C-reactive protein level of 2 mg or more per liter. The trial compared three doses of canakinumab (50 mg, 150 mg, and 300 mg, administered subcutaneously every 3 months) with placebo. The primary efficacy end point was nonfatal myocardial infarction, nonfatal stroke, or cardiovascular death. RESULTS: At 48 months, the median reduction from baseline in the high-sensitivity C-reactive protein level was 26 percentage points greater in the group that received the 50-mg dose of canakinumab, 37 percentage points greater in the 150-mg group, and 41 percentage points greater in the 300-mg group than in the placebo group. Canakinumab did not reduce lipid levels from baseline. At a median follow-up of 3.7 years, the incidence rate for the primary end point was 4.50 events per 100 person-years in the placebo group, 4.11 events per 100 person-years in the 50-mg group, 3.86 events per 100 person-years in the 150-mg group, and 3.90 events per 100 person-years in the 300-mg group. The hazard ratios as compared with placebo were as follows: in the 50-mg group, 0.93 (95% confidence interval [CI], 0.80 to 1.07; P = 0.30); in the 150-mg group, 0.85 (95% CI, 0.74 to 0.98; P = 0.021); and in the 300-mg group, 0.86 (95% CI, 0.75 to 0.99; P = 0.031). The 150-mg dose, but not the other doses, met the prespecified multiplicity-adjusted threshold for statistical significance for the primary end point and the secondary end point that additionally included hospitalization for unstable angina that led to urgent revascularization (hazard ratio vs. placebo, 0.83; 95% CI, 0.73 to 0.95; P = 0.005). Canakinumab was associated with a higher incidence of fatal infection than was placebo. There was no significant difference in all-cause mortality (hazard ratio for all canakinumab doses vs. placebo, 0.94; 95% CI, 0.83 to 1.06; P = 0.31). Conclusions: Antiinflammatory therapy targeting the interleukin-1β innate immunity pathway with canakinumab at a dose of 150 mg every 3 months led to a significantly lower rate of recurrent cardiovascular events than placebo, independent of lipid-level lowering. (Funded by Novartis; CANTOS ClinicalTrials.gov number, NCT01327846.