Silicic acid controls the production of diatoms, a predominant phytoplankton in the Southern Ocean. Diatoms are major contributors to the biological carbon pump, which is particularly active in the Southern Ocean as well as in areas naturally enriched in iron, such as around the Kerguelen Plateau. This study evaluates the factors controlling the biogeochemical cycle of Si and its dynamics in this area and how it is impacted by the island mass effect using the Si isotopic signatures of both dissolved and biogenic Si. While subsurface winter waters have similar delta Si-30 signatures and dissolved Si concentrations, surface delta Si-30 and dissolved Si values are different between stations. We show that this results from both (i) a different degree of dissolved Si utilization by silicifiers from winter water as the main Si source and (ii) an additional significant Si source to dissolved Si in the mixed layer from lithogenic Si dissolution for areas under the influence of the shelf. Indeed, the delta Si-30(DSi) signatures near the islands are homogeneous and lighter by -0.33 parts per thousand +/- 0.07 parts per thousand in the mixed layer compared to the outside plateau station. We estimate such lithogenic Si contribution to dissolved Si at 2.9 +/- 1.8 mu mol L-1 for a corresponding specific flux of 3.7 +/- 2.3 x 10(6) mol km(-2) yr(-1) in shallow areas around Heard and McDonald Islands (< 100 m). This Si dissolution flux per surface area is among the highest in the ocean and has a traceable biogeochemical impact over the Northern Kerguelen Plateau. It is likely due to the active volcanic nature of these islands combined with subglacial erosion on Heard.

Marine microbes are strongly interrelated to trace metals in the ocean. How the availability of trace metals selects for prokaryotic taxa and the potential feedback of microbial processes on the trace metal distribution in the ocean remain poorly understood. We investigate here the potential reciprocal links between diverse prokaryotic taxa and iron (Fe), manganese (Mn), copper (Cu), and nickel (Ni) as well as apparent oxygen utilization (AOU) across 12 well-defined water masses in the Southern Indian Ocean (SWINGS-South West Indian Ocean GEOTRACES GS02 Section cruise). Applying partial least square regression (PLSR) analysis, we show that the water masses are associated with particular latent vectors that are a combination of the spatial distribution of prokaryotic taxa, trace elements, and AOU. This approach provides novel insights on the potential interactions between prokaryotic taxa and trace metals in relation to organic matter remineralization in distinct water masses of the ocean.

The formation of dense Brine-enriched Shelf Water (BSW) in Storfjorden is analyzed during Winter 2016-2017 from mooring observations, a polynya model nudged to satellite observations, and an original BSW production model. The ice season was two months shorter than average, yet 44.2 km3 ${\text{km}}<^>{3}$ of sea ice were formed, in line with estimates for the period preceding the atlantification of the Barents Sea in the mid-2000s: A thinner, more fragile ice may favor polynya openings and frazil ice production. A saline specimen of BSW was produced in large volumes, corresponding to an annual mean transport of 0.042 Sv, larger than previous estimates. The important production is due to the preconditioning of the polynya with a more saline source water, exceeding the pre-2005 values by 0.37. The BSW overflow was observed on the West Spitsbergen shelf slope from hydrographic sections down to 750 m, thus entering the Norwegian Sea Deep Water layer. Its core temperature was about 1 degrees $1{}<^>{\circ}$C warmer than the pre-2005 values owing to the entrainment of a warmer water in Storfjordrenna, suggesting that a part of the excess surface heat of the Barents Sea could be exported into the deep ocean. Overall our results suggest that dense water formation in the Storfjorden polynya may not, at least for now, be hampered by the atlantification of the Barents Sea, and perhaps even temporarily favored by the more saline source water. Anomalous atmospheric warming during the Winter-Spring may however disrupt the production, as was observed 1 year before. Sea-ice extent has strongly declined in the Barents Sea since the mid-2000s. The sea has also become warmer and saltier, a phenomenon referred to as atlantification. This raises concerns regarding the future of dense water production in coastal polynyas, an essential cog in the climate machine. Polynyas work as ice factories, releasing large quantities of salt in the ocean, which can lead surface waters to cascade into the deep ocean when dense enough. We analyze dense water production in Winter 2016-2017 in the Storfjorden polynya (Svalbard) from a time series of hydrographic observations and an ice production model. Despite a shorter freezing season, the ice production and salt release remained average, while preconditioning with a more saline source water permitted the production of a particularly saline dense water in large volumes. The dense bottom plume was observed to sink into the deep ocean. It was warmer than in the past, suggesting that part of the excess surface heat could be stored at depth. Overall our results suggest that dense water production may not, at least for now, be hampered by the atlantification of the Barents Sea, unless strongly anomalous winter atmospheric warming disrupts ice production, as observed 1 year before. A simple model to estimate the production of dense water from hydrographic time series and salt forcing is developed Preconditioning of the polynya with saltier source water promoted the production of dense Brine-enriched Shelf Water (BSW) in 2017 despite an average ice production The BSW overflow was observed to sink down to the Deep Water layer: It was warmer than in observations prior to the atlantification

Hydrothermal vents have been shown to be important vectors for various chemical elements into the ocean. However, both the intensity of the chemical fluxes associated with these systems and the fate of the chemical elements along the plume are still largely overlooked. At two stations located above the South West Indian Ridge (SWIR), we investigate the distributions of the Ra quartet (223Ra, 224Ra, 226Ra and 228Ra) and 227Ac that have been used as tracers of hydrothermal activity. While the vertical distributions of 226Ra, 228Ra and 227Ac do not show a clear enrichment at depth, unusual signatures of excess 223Ra and 224Ra near the seafloor are attributed to the presence of a hydrothermal activity. The discrepancy observed between the different isotopes is attributed to different chemical reactivity when seawater circulates within the crust and/or to different regeneration rates within the fluid. A 1D diffusion model applied to the vertical profiles of short-lived Ra isotopes provided an estimation of the vertical eddy diffusivity coefficients (KZ) between 38 cm2 s-1 and 149 cm2 s- 1. These high values suggest strong mixing likely favored by the complex bathymetry in the region. By combining these KZ with the vertical gradient of dissolved Fe (dFe), we estimate a vertical flux of dFe that ranges from 139 to 1173 nmol m- 2 d-1. These results confirm that low -expansion -rate ridges could be significant sources of dFe to the deep ocean.

Iron (Fe) and manganese (Mn) are crucial micronutrients that limit oceanic primary productivity in the Southern Ocean. It has been recently suggested that hydrothermal activity may be an important source of oceanic dissolved iron, yet, this contribution is still not fully understood and only one active hydrothermal site has been reported on the Southwest Indian Ridge (SWIR), south of 40 degrees S. Using a multi-proxy approach, this study demonstrates the occurrence of hydrothermal venting on the SWIR in the near vicinity of the location 44 degrees 51.690 S, 36 degrees 10.460 E, which is likely to be a low or moderately high temperature fluid. Indeed, we report high values of dissolved methane to manganese ratios (up to 11.1 +/- 1.2 mol mol-1), low particulate iron (pFe) and manganese (pMn) concentrations (with maximum values of 0.7 nmol L-1 and 0.06 nmol L-1, respectively) associated with the presence of few oxyhydroxides, as well as high 223Radium (Ra) and 224Ra activities near the seafloor. The Fe and Mn data revealed a significant enrichment at depths influenced by hydrothermal circulation on the seafloor, within the Upper Circumpolar Deep Water. Dissolved Fe (dFe) and dissolved Mn (dMn) concentrations were enriched by 3- and 7-fold, respectively, and pFe and pMn by 2- and 1.5-fold, respectively, compared to a reference station located outside the SWIR. They were however lower than concentrations reported so far near high temperature vents, suggesting a weaker influence of this hydrothermal system on deep Fe and Mn reservoirs. We show that a large fraction of the dFe could be stabilized by organic complexation with humic substances (eHS, estimated 27-60% of dFe). High prokaryotic abundance related to the proximity of the hydrothermal vent suggests that other Fe-complexing ligands of biological origin might also stabilize Fe in its dissolved form. Collectively, these measurements integrated within the concept of a "multi-proxy approach", helped painting a more detailed picture of the complex interactions and processes in this region of the SWIR. Although the system is a source of both dFe and dMn to the deep ocean, the low current velocities and the bathymetry likely limit the fertilization of surface water by dFe and dMn along this section of the SWIR.

The intensity and spectrum of light under Arctic sea ice, key to the energy budget and primary productivity of the Arctic Ocean, are tedious to observe. Earth System Models (ESMs) are instrumental in understanding the large-scale properties and impacts of under-ice light. To date, however, ESM parameterizations of radiative transfer have been evaluated with a few observations only. From observational programs conducted over the past decade at four locations in the Northern Hemisphere sea ice zone, 349 observational records of under-ice light and coincident environmental characteristics were compiled. This data set was used to evaluate seven ESM parameterizations. Snow depth, melt pond presence and, to some extent, ice thickness explain the observed variance in light intensity, in agreement with previous work. The effects of Chlorophyll-a are also detected, with rather low intensity. The spectral distribution of under-ice light largely differs from typical open ocean spectra but weakly varies among the 349 records except for a weak effect of snow depth on the blue light contribution. Most parameterizations considered reproduce variations in under-ice light intensity. Large errors remain for individual records, on average by a factor of similar to 3, however. Skill largely improves if more predictors are considered (snow and ponds in particular). Residual errors are attributed to missing physics in the parametrizations, inconsistencies in the model-observation comparison protocol, and measurement errors. We provide recommendations to improve the representation of light under sea ice in the ice-ocean model NEMO, which may also apply to other ESMs and help improve next-generation ESMs.

Storfjorden, Svalbard, hosts a polynya in winter and is an important source region of Brine-enriched Shelf Water (BSW) that, if dense enough, feeds the Arctic Ocean deep water reservoir. Changes in the BSW production may thus have far-reaching impacts. We analyze the water mass distribution and circulation in Storfjorden and the trough south of it, Storfjordrenna, using hydrographic sections occupied in July 2016, following a winter characterized by the lowest ice coverage recorded in the Barents Sea. These observations reveal an unusual hydrographic state, characterized at the surface by the near absence of Melt Water and Storfjorden Surface Water, replaced by a saltier water mass. At depth, BSW (maximum salinity of 34.95) was found from the bottom up to 90 m, above the 120-m deep sill at the mouth to Storfjordrenna. However, no gravity driven overflow was observed downstream of the sill: the dome of BSW remained locked over the depression in a cyclonic circulation pattern consistent with a stratified Taylor column. Observations further reveal a previously unreported intrusion of Atlantic Water (AW) far into the fjord, promoting isopycnal mixing with entrapped Arctic Water. This intrusion was possibly favored by positive wind stress curl anomalies over Svalbardbanken and Storfjordrenna. The bottom plume exiting Storfjordrenna was weak, carrying Polar Front Water rather than BSW, too light to sink underneath the AW layer at Fram Strait. Whether Storfjorden switched durably to a new hydrographic state, following the observed Atlantification of the Barents Sea after 2005, remains to be established.

The Copernicus Sentinel-3 Surface Topography Mission (STM) Land Altimetry provides valuable surface elevation information over inland waters, sea ice, and land ice, thanks to its synthetic aperture radar (SAR) altimeter and its orbit that covers high-latitude polar regions. To ensure that these measurements are reliable and to maximise the return on investment, adequate validation of the geophysical retrieval methods, processing algorithms, and corrections must be performed using independent observations. The EU-ESA project St3TART (started July 2021) aims to generalise the concept of Fiducial Reference Measurements (FRMs) for the Copernicus Sentinel-3 STM. This work has gathered existing data, made new observations during field campaigns, and ensured that these observations meet the criteria of FRM standards so that they can be used to validate Sentinel-3 STM Land Altimetry products operationally. A roadmap for the operational provision of the FRM, including the definition, consolidation, and identification of the most relevant and cost-effective methods and protocols to be maintained, supported, or implemented, has been developed. The roadmap includes guidelines for SI traceability, definitions of FRM measurement procedures, processing methods, and uncertainty budget estimations.

LOCEAN laboratory of the Pierre and Simon Laplace Insitute (IPSL) is in charge of a number of scientific projects and measurement campaigns that result in a large flow of heterogeneous oceanographic data managed at LOCEAN. The data are of various origins and include in situ data from buoys, ships, moorings, marine mammals and satellite missions for salinity, altimetry, ocean color, temperature. LOCEAN also has an instrumental development team that designs and deploys buoys in various parts of the global ocean, with a need to receive and track the data in the near-real time. The data PIs can be involved in different research groups and projects, and while focusing on providing their data, they might need to collaborate with other teams providing complementary datasets. To address these needs, the INSITUDE platform is developed at LOCEAN with these goals in mind: (1) receive, manage, track in the near-real time, and explore diverse data; (2) assist scientific experts in the data quality control; (3) facilitate cross-uses of insitu and satellite data available at LOCEAN. The software consists of four components: (1) Django application for the meta-data management; (2) Data processing software (Python); (3) Flask application for server-side interactions with the database; (4) Interactive data exploration/validation front-end. The basic workflow involves the following steps: (1) The user specifies the relevant meta-data using the web interface of the Django application; the meta-data database is thus updated; (2) The processing core is launched automatically at regular times during a day: it reads the meta-data from the database, queries the mailboxes and/or external web services for the data requested, receives, decodes and processes the data, and fills the measurements database. It also generates ASCII data files for selected datasets, which can be downloadable via dedicated web pages or can be used for processing with external user programs (e.g. matlab or python scripts); (3) The data stored in the measurements database can be interactively explored using DataViewer applications, allowing zoomable views of time series, vertical profiles, and trajectories shown on the virtual globe. Data from different campaigns and for different variables can be viewed together. The quality control assistant allows experts to seamlessly validate the data by assigning quality flags to selected data points or regions, optionally after computing relevant statistics. The validated data can then be visualized and saved based on desired quality flag values. The INSITUDE platform facilitates data sharing across multiple teams and collaborations between data providers and data experts, researchers and engineers, enabling research projects focused on cross-exploration of various datasets, studies of processes involving both in situ and satellite data, and interpretation of in situ data in a larger-scale context owing to the satellite data. The system offers centralized intuitive acquisition control and access to the data received, along with the related meta-data (projects, campaigns, buoys, people, etc.), facilitates data quality control/validation. The INSITUDE platform is currently used at LOCEAN and can be deployed in data centers of national data infrastructures, such as the French ODATIS/DATA TERRA.

The Soil Moisture and Ocean Salinity (SMOS) satellite is performing systematic L-band observations since 2009, allowing a large number of science and operational applications. Several recent studies have shown the need of the continuity of L-band observations, in particular with an increased angular resolution. In this contribution, two instrumental concepts are presented to reach native resolutions of 5–10 km. In addition, using airborne data, it is also shown that the accuracy of downscaling coarser resolution L-band data to 5–10 km using a high resolution auxiliary data set, is significantly lower than that of native high resolution observations.

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.Thepaperstarts 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. (cid:1) 2021 COSPAR. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/ by-nc-nd/4.0/).

The Green Edge initiative was developed to investigate the processes controlling the primary productivity and fate of organic matter produced during the Arctic phytoplankton spring bloom (PSB) and to determine its role in the ecosystem. Two field campaigns were conducted in 2015 and 2016 at an ice camp located on landfast sea ice southeast of Qikiqtarjuaq Island in Baffin Bay (67.4797∘ N, 63.7895∘ W). During both expeditions, a large suite of physical, chemical and biological variables was measured beneath a consolidated sea-ice cover from the surface to the bottom (at 360 m depth) to better understand the factors driving the PSB. Key variables, such as conservative temperature, absolute salinity, radiance, irradiance, nutrient concentrations, chlorophyll a concentration, bacteria, phytoplankton and zooplankton abundance and taxonomy, and carbon stocks and fluxes were routinely measured at the ice camp. Meteorological and snow-relevant variables were also monitored. Here, we present the results of a joint effort to tidy and standardize the collected datasets, which will facilitate their reuse in other Arctic studies. The dataset is available at https://doi.org/10.17882/59892 (Massicotte et al., 2019a).

Winter to summer CO(2)dynamics within landfast sea ice in McMurdo Sound (Antarctica) were investigated using bulk ice pCO(2)measurements, air-snow-ice CO(2)fluxes, dissolved inorganic carbon (DIC), total alkalinity (TA), and ikaite saturation state. Our results suggest depth-dependent biotic and abiotic controls that led us to discriminate the ice column in three layers. At the surface, winter pCO(2)supersaturation drove CO(2)release to the atmosphere while spring-summer pCO(2)undersaturation led to CO(2)uptake most of the time. CO(2)fluxes showed a diel pattern superimposed upon this seasonal pattern which was potentially assigned to either ice skin freeze-thaw cycles or diel changes in net community production. In the ice interior, the pCO(2)decrease across the season was driven by physical processes, mainly independent of the autotrophic and heterotrophic phases. Bottom sea ice was characterized by a massive biomass build-up counterintuitively associated with transient heterotrophic activity and nitrate plus nitrite accumulation. This inconsistency is likely related to the formation of a biofilm. This biofilm hosts both autotrophic and heterotrophic activities at the bottom of the ice during spring and may promote calcium carbonate precipitation.

23 Winter to summer CO2 dynamics within landfast sea ice in McMurdo Sound (Antarctica) were 24 investigated using bulk ice pCO2 measurements, air-snow-ice CO2 fluxes, dissolved inorganic 25 carbon (DIC), total alkalinity (TA) and ikaite saturation state. Our results suggest depth26 dependent biotic and abiotic controls that led us to discriminate the ice column in three layers. At 27 the surface, winter pCO2 supersaturation drove CO2 release to the atmosphere while spring28 summer pCO2 undersaturation led to CO2 uptake most of the time. CO2 fluxes showed a diel 29 pattern superimposed upon this seasonal pattern which was potentially assigned to either ice skin 30 freeze-thaw cycles or diel changes in net community production. In the ice interior, the pCO2 31 decrease across the season was driven by physical processes, mainly independent of the 32 autotrophic and heterotrophic phases. Bottom sea ice was characterized by a massive biomass 33 build-up counterintuitively associated with transient heterotrophic activity and nitrate plus nitrite 34 accumulation. This inconsistency is likely related to the formation of a biofilm. This biofilm 35 hosts both autotrophic and heterotrophic activities at the bottom of the ice during spring and may 36 promote calcium carbonate precipitation. 37 Plain Language Summary 38 Sea ice participates actively in the regional cycling of CO2 both as a source and a sink at 39 different times of the year depending on ice physics, ice chemistry and ice trophic status 40 (autotrophic vs heterotrophic). We identified the key processes driving the CO2 dynamics in each 41 sea ice layer (surface, interior and bottom) from McMurdo Sound (Antarctica) from late winter 42 to summer. At the surface, CO2 release from the ice to the atmosphere occurred in late winter 43 while CO2 uptake occurred in summer. Superimposed upon this seasonal pattern, we observed a 44 diurnal pattern with both release and uptake occurring over 24 h period. This diurnal pattern can 45 be related to physical processes (nocturnal freeze-up and diurnal melting) or biotic processes 46 (autotrophy or heterotrophy). In the ice interior, a succession of autotrophic and heterotrophic 47 phases took place. At the sea ice bottom, a particular assemblage of microbial cells and organic 48 matter, called biofilm, enabled the accumulation of biomass and nitrate plus nitrite 49 simultaneously leading to both autotrophic and heterotrophic activities. In addition, this biofilm 50 is suggested to promote calcium carbonate precipitation. 51

Saroma-ko Lagoon, located on the Okhotsk Sea coast of Hokkaido, is seasonally covered by flat, homogeneous, easily accessible and safe sea ice. As such, it proves a very useful experimental site for the study of sea ice processes, the inter-comparison of methods, the testing of equipment, and the training of researchers new to the Polar regions. In this contribution, we describe a physical, chemical, and ecosystem survey at Saroma-ko Lagoon, conducted over February 23-28, 2019 under the auspices of the SLOPE2019 (Saroma-ko Lagoon Observations for sea ice Physico-chemistry and Ecosystems 2019) program. Sea ice cores were collected to examine temperature, salinity, oxygen isotopic ratio, thin sections, and chemical and biological parameters such as carbonate chemistry, CH4, nutrients, chlorophyll a concentrations, and ice algae community assemblage. Broadband and spectral irradiance measurements were carried out above/under the sea ice, and different sensors were inter-compared at close positions and environments. Equipment such as spectrometers, air-sea ice CO2/CH4 flux chamber, and under-ice turbulent heat flux systems were tested for future Arctic and Antarctic expeditions. Finally, an artificial pool was dug into the sea ice to understand the effect of snow particles on ice growth and to compare the gas exchange process over sea ice with an ice-free water surface. Our SLOPE2019 field campaign activities provided useful information for inter-comparison work and future sea ice research in the polar oceans.

The European Space Agency (ESA) Soil Moisture and Ocean Salinity (SMOS) has been providing the longest consistent data record of passive L-band (1.4 GHz) observations for more than ten years. SMOS, as well as the NASA missions SMAP and Aquarius have demonstrated the interest of L-band observations for land, ocean and cryosphere studies. The continuity of L-band observations must be assured taking into account that the spatial resolution (∼ 40 km) of SMOS and SMAP is too coarse for some applications. Disaggregation strategies can be implemented but using airborne data, we show that the quality of the downscaled data cannot match that of an instrument with higher native resolution. The goal of the SMOS-HR (High Resolution) mission is to ensure the continuity of L-band observations while increasing the native resolution to 10 km. SMOS-HR will carry an array of ∼ 230 antennas to perform aperture synthesis. The antenna distribution has been optimized to reduce the aliasing in the reconstructed images and SMOS-HR will incorporate advanced on-board Radio Frequency Interferences (RFI) mitigation techniques.

Recent studies have discovered an intriguing nonstationary relationship between El Ninõ–Southern Oscillation (ENSO) and the Western Pacific (WP) teleconnection pattern, one of the most prominent winter atmospheric circulation patterns in the North Pacific, with a regime-dependent interdecadal modulation of significant and insignificant correlations. However, the physical process underlying the observed nonstationary ENSO-WP relationship is a puzzle and remains to be elucidated, which is also essential for clarifying the still-debated nontrivial issue on whether the WP is directly forced by ENSO or by midlatitude storm tracks-driven intrinsic processes. Based on empirical orthogonal function (EOF) analysis of the upper-tropospheric teleconnection patterns and associated Rossby wave sources (RWS), we show that the nonstationarity in question is due to the regime-dependent constructive or destructive interference in meridional overturning circulation between the two leading EOFs of RWS best correlated with ENSO and WP, respectively. The observed insignificant correlation between ENSO and the WP after the 1988 regime shift can be explained by interrupted teleconnection between the tropics and high latitudes due to the collapse of the subtropical bridge pillar in the jet entrance region, consequence of the destructive interference. This suggested interference mechanism related to the regime-dependent upper-level RWS fields has significant implications for resolving the puzzle that hinders better understanding of decadal regime behaviors of the climate system in the North Pacific.

Sustained observations of environmental conditions in the North Pole region are critical to understanding the changing Arctic Ocean. The Transpolar Drift conduit of sea ice and freshened upper-ocean waters across the Arctic Ocean passes over the North Pole region on its way to the North Atlantic through Fram and Nares Straits. The exported ice and freshened water stratifies the sub-Arctic seas and limits the vertical convection that ventilates the world ocean. Key variables such as ice thickness, bottom pressure, and hydrography in the North Pole region are thus sensitive indicators of changes over the whole Arctic Basin and how these affect the global ocean. Drifting buoys installed in the North Pole region by Great Britain, Canada, France, Germany, Japan, and the U.S. address what would otherwise be a dearth of ocean, ice, and atmosphere observations in the central Arctic. A suite of satellite remote sensing tools such as ICESat/ICESat-2 from the U.S., GRACE from the U.S. and Germany, and CryoSat2 from the European Union extend the conclusions from central Arctic Ocean in situ observations to other regions. Detecting and understanding climate change requires observations over decadal and longer scales. We propose an international program as the key to sustaining these observations in the North Pole region. Such an international program would help immeasurably by 1) facilitating financial sharing of the burden of long-term measurements among several nations, (2) reducing logistics costs through economies of scale, and 3) providing a buffer against national funding, logistics, and geopolitical difficulties.

To understand the upper-ocean thermal variability in the Kuroshio-Oyashio Extension (KOE) region, the upper 400 m heat budget in the western North Pacific is analyzed for the 1981-2013 period using outputs from a high resolution (1/128) ocean general circulation model. Winter heat storage rate on interannual to decadal time scales is mainly determined by oceanic heat advection rather than by net air-sea heat flux. The role of heat advection becomes particularly prominent and widely spread over the entire western North Pacific after the 1990 regime shift in association with the reduced variability of surface heat flux caused by weakened SST variability. The net heat flux acts to dampen temperature anomalies caused by the ocean dynamics. The ocean dynamics causing the upper-ocean heat storage rate is principally associated with the meridional shift of the Oyashio Extension front, which is significantly correlated with both the West Pacific and Pacific-North America teleconnection patterns.