Updated Arctic melt pond fraction dataset and trends 2002–2023 using ENVISAT and Sentinel-3 remote sensing data

Abstract. Melt ponds on the Arctic sea ice affect the radiative balance of the region as they introduce darkening of the sea ice during the Arctic summer. Temporal and spatial extent of the ponding as well as its amplitude reflect the state of the Arctic sea ice and are important for our understanding of the Arctic sea ice change. Remote sensing retrievals of melt pond fraction (MPF) provide information both on the present state of the melt pond development as well as its change throughout the years, which is a valuable information in the context of climate change and Arctic amplification.

In this work, we transfer the earlier published Melt Pond Detector remote sensing retrieval (MPD) to the Ocean and Land Colour Instrument (OLCI) data onboard the Sentinel-3 satellite and so complement the existing Medium Resolution Imaging Spectrometer (MERIS) MPF dataset (2002–2011) from Environmental Satellite (ENVISAT) with the recent data (2017–present). To evaluate the bias of the MPF product, comparisons to Sentinel-2 MultiSpectral Instrument (MSI) high resolution satellite imagery are presented, in addition to earlier published validation studies. Both MERIS and OLCI MPD tend to overestimate the small MPFs, which can be attributed to the presence of water saturated snow and sea ice before melt onset. Good agreement for middle range MPF is observed, and the areas of exceptionally high MPF = 100 % are recognized as well.

The earlier published MERIS MPFs (2002–2011) were reprocessed using an improved cloud clearing routine and together with the recent Sentinel-3 data provide an internally consistent dataset, which allows to analyse the MPF development in the past 20 years. Although the total summer hemispheric MPF trend is moderate with +0.75 % per decade, the regional weekly MPF trends display pronounced dynamic and range from −10 % to as high as +20 % per decade, depending on the region. We conclude on the following effects:

• the global Arctic melt onset shifted towards spring by at least 2 weeks, with the melt onset happening in late May in the recent years as compared to early-mid June in the beginning of the dataset.
•  there is a change of the melt onset regime in the recent years, with East Siberian and Laptev Sea dominating the melt onset and not the Beaufort Gyre region as before.
• the Central Arctic, North Greenland and CAA show signs of increasing first year ice (FYI) fraction in the recent years.

The daily gridded MPF averages are available at the webpage of the Institute of Environmental Physics, University of Bremen, as a historic dataset for the ENVISAT data, and as ongoing operational processing for the Sentinel-3 data.