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Bathymetry (seafloor depth), is a critical parameter providing the geospatial context for a multitude of marine scientific studies. Since 1997, the International Bathymetric Chart of the Arctic Ocean (IBCAO) has been the authoritative source of bathymetry for the Arctic Ocean. IBCAO has merged its efforts with the Nippon Foundation-GEBCO-Seabed 2030 Project, with the goal of mapping all of the oceans by 2030. Here we present the latest version (IBCAO Ver. 4.0), with more than twice the resolution (200 × 200 m versus 500 × 500 m) and with individual depth soundings constraining three times more area of the Arctic Ocean (∼19.8% versus 6.7%), than the previous IBCAO Ver. 3.0 released in 2012. Modern multibeam bathymetry comprises ∼14.3% in Ver. 4.0 compared to ∼5.4% in Ver. 3.0. Thus, the new IBCAO Ver. 4.0 has substantially more seafloor morphological information that offers new insights into a range of submarine features and processes; for example, the improved portrayal of Greenland fjords better serves predictive modelling of the fate of the Greenland Ice Sheet.Measurement(s)depthTechnology Type(s)digital curationFactor Type(s)geographic locationSample Characteristic - Environmentocean floorSample Characteristic - LocationArctic OceanMachine-accessible metadata file describing the reported data: 10.6084/m9.figshare.12369314

THE ice cores recovered from central Greenland by the GRIP 1,2 and GISP2 3 projects record 22 interstadial (warm) events during the part of the last glaciation spanning 20–105 kyr before present. The ice core from Vostok, east Antarctica, records nine interstadials during this period 4,5 . Here we explore links between Greenland and Antarctic climate during the last glaciation using a high-resolution chronology derived by correlating oxygen isotope data for trapped O 2 in the GISP2 and Vostok cores. We find that interstadials occurred in east Antarctica whenever those in Greenland lasted longer than 2,000 years. Our results suggest that partial deglaciation and changes in ocean circulation are partly responsible for the climate teleconnection between Greenland and Antarctica. Ice older than 115 kyr in the GISP2 core shows rapid variations in the δ 18 O of O 2 that have no counterpart in the Vostok record. The age–depth relationship, and thus the climate record, in this part of the GISP2, core appears to be significantly disturbed.

In our earlier paper (Dickson and Wheeler 1993), we question the existence of a latitudinal gradient in integrated chlorophyll a (Chl a) concentrations between subtropical and subarctic waters. Our results indicate that a significant fraction of the Chl a in subtropical waters passed through the GF/F filters but was retained by 0.2- mu m Nucleopore filters. Comparison of the calculated gradients in integrated Chl a (Table 1) shows that the relatively steep latitudinal gradients observed for Chl a retained on GF/C and GF/F filters are diminished when results are calculated for Chl a retained on 0.2- mu m filters.

PN‐specific, absolute, and Chl a‐specific nitrate uptake rates were measured during two upwelling seasons and one winter off Oregon. Although PN‐specific and absolute uptake rates showed no dependence on nitrate concentration, Michaelis‐Menten kinetics applied when the uptake rates were normalized to Chl a. Chl a‐specific nitrate uptake rates were saturated when nitrate concentrations were > 5 M. Uptake rates decreased in response to either low nitrate concentrations or when extremely high phytoplankton biomass caused shading. PN‐ and Chl a‐specific uptake rates were similar when Chl a concentrations were ≥ 4 µg liter−1 and phytoplankton N comprised most of the PN (particulate organic N) pool. When Chl a was <4 µg liter−1, however, phytoplankton N accounted for only 20–30% of the PN, and estimated phytoplankton‐specific uptake was 5‐fold greater than PN‐specific uptake rates. These results suggest that observed temporal changes in PN‐specific nitrate uptake rates reflect variations in phytoplankton biomass rather than changes in phytoplankton‐specific activity.

Knowledge about seafloor depth, or bathymetry, is crucial for various marine activities, including scientific research, offshore industry, safety of navigation, and ocean exploration. Mapping the central Arctic Ocean is challenging due to the presence of perennial sea ice, which limits data collection to icebreakers, submarines, and drifting ice stations. The International Bathymetric Chart of the Arctic Ocean (IBCAO) was initiated in 1997 with the goal of updating the Arctic Ocean bathymetric portrayal. The project team has since released four versions, each improving resolution and accuracy. Here, we present IBCAO Version 5.0, which offers a resolution four times as high as Version 4.0, with 100 × 100 m grid cells compared to 200 × 200 m. Over 25% of the Arctic Ocean is now mapped with individual depth soundings, based on a criterion that considers water depth. Version 5.0 also represents significant advancements in data compilation and computing techniques. Despite these improvements, challenges such as sea-ice cover and political dynamics still hinder comprehensive mapping. Measurement(s) Depth Technology Type(s) Digital curation Factor Type(s) Geographic location Sample Characteristic - Environment Ocean floor Sample Characteristic - Location Arctic Ocean

Chlorophyll a concentrations were measured as a function of depth from 28 to $48\\circ N$ along $152\\circ W$ in March 1991 with Whatman GF/F and $0.2-\\mum$ Nuclepore filters. Surface Chl a concentrations measure with $0.2-\\mum$ Nuclepore filters were up to fourfold higher than those measured with Whatman GF/F filters. The largest difference between the two filter types was found in subtropical waters, where picoplankton were major constituent of the phytoplankton assemblage. Chl a concentrations integrated from 0 to 175 m showed a threefold increase $(9-26 mg Chl a m^-2)$ between 28 and $48\\circ N$ when Whatman GF/F filters were used. However, integrated Chl a concentrations based on measurements with $0.2-\\mum$ Nuclepore filters were nearly constant $(25-31 mg Chl a m^-2)$ over the transect. These results lead us to question the existence of previously reported latitudinal gradients in integrated Chl a concentrations in the North Pacific Ocean.

PN-specific, absolute, and Chl a-specific nitrate uptake rates were measured during two upwelling seasons and one winter off Oregon. Although PN-specific and absolute uptake rates showed no dependence on nitrate concentration, Michaelis-Menten kinetics applied when the uptake rates were normalized to Chl a. Chl a-specific nitrate uptake rates we saturated when nitrate concentrations were $> 5 \\mu M$. Uptake rates decreased in response to either low nitrate concentrations or when extremely high phytoplankton biomass caused shading. PN-and Chl a-specific uptake rates were similar when Chl a concentrations were $\\geq 4 \\mu g liter^-1$ and phytoplankton N comprised most of the Pn (particulate organic N) pool. When Chl a was $<4 \\mu g liter^-1$, however, phytoplankton N accounted for only 20-30% of the PN, and estimated phytoplankton-specific uptake was 5-fold greater than PN-specific uptake rates. These results suggest that observed temporal changes in PN-specific nitrate uptake rates reflect variations in phytoplankton biomass rather than changes in phytoplankton-specific activity.

Ammonium uptake and regeneration rates were measured in time course experiments with 15N as a tracer. Both ammonium uptake and regeneration rates measured over 12 to 18 h remained essentially constant. However, as the length of the incubations increased the amount of usable data decreased dramatically due to substrate depletion and recycling of 15N. Mass balance calculations indicated that 22 to 51 % of the ammonium removed from the dissolved pool was not recovered in the particulate fraction. This appeared to be a more serious problem at 0 and 8 m (47 %) than at 25 m (22%). As a result, ammonium uptake rates were probably underestimated. At 0, 12, and 20 m uptake rates either balanced or exceeded regeneration rates, while at 8 and 25 m net regeneration occurred. The fastest rates were measured during upwelling-induced phytoplankton blooms, intermediate rates characterized post-bloom conditions and the lowest rates coincided with an active upwelling event. Ammonium uptake rates were highest during the upwelling season (11 to 17 mmol N m−2 d−1) and lowest during the non-upwelling season (3 mmol N m−2 d−1), whereas regeneration rates did not differ significantly between seasons (11 to 20 mmol N m−2 d−1).