Some ecosystems can undergo abrupt transformation in response to relatively small environmental change. Identifying imminent "tipping points" is crucial for biodiversity conservation, particularly in the face of climate change. Here we describe a tipping point mechanism likely to induce widespread regime shifts in polar ecosystems. Seasonal snow and ice cover periodically block sunlight reaching polar ecosystems, but the effect of this on annual light depends critically on the timing of cover within the annual solar cycle. At high latitudes sunlight is strongly seasonal, and ice-free days around the summer solstice receive orders of magnitude more light than those in winter. Early melt that brings the date of ice-loss closer to midsummer will cause an exponential increase in the amount of sunlight reaching some areas per year. This is likely to drive ecological tipping points in which primary producers (plants and algae) flourish and out-compete dark-adapted communities. We demonstrate this principle on Antarctic shallow seabed ecosystems, which our data suggest are sensitive to small changes in the timing of sea-ice loss. Algae respond to light thresholds that are easily exceeded by a slight reduction in sea-ice duration. Earlier sea-ice loss is likely to cause extensive regime-shifts in which endemic shallow-water invertebrate communities are replaced by algae, reducing coastal biodiversity and fundamentally changing ecosystem functioning. Modeling shows that recent changes in ice and snow cover have already transformed annual light budgets in large areas of the Arctic and Antarctic, and both aquatic and terrestrial ecosystems are likely to experience further significant change in light. The interaction between ice loss and solar irradiance renders polar ecosystems acutely vulnerable to abrupt ecosystem change, as light-driven tipping points are readily breached by relatively slight shifts in the timing of snow and ice loss. This archive contains data and statistical code for the article: Graeme F. Clark, Jonathan S. Stark, Emma L. Johnston, John W. Runcie, Paul M. Goldsworthy, Ben Raymond and Martin J. Riddle (2013) Light-driven tipping points in polar ecosystems. Global Change Biology Data and code are organised into folders according to figures in the article. See the article for a full description of methods. Statistical code was written in R v. 2.15.0. In data files, rows are samples and columns are variables. Details for numerical variables in each data file are listed below. Figures 7 and 8 were made in MATLAB and code is not provided. Figure 1: rad_data.csv Solar irradiance data derived from: Suri M, Hofierja J (2004) A new GIS-based solar radiation model and its application to photovoltaic assessments. Transactions in GIS 8: 175-190. Figure 2: Fig. 2c.1.csv Light: Measured light at the seabed per day (mol photons m-2 d-1). Figure 2: Fig. 2c.2.csv Light: Measured light at the seabed per day (mol photons m-2 d-1). Light.mod.p: Light at the seabed per day (mol photons m-2 d-1) predicted from modeled seasonal variation. Figure 2: Fig. 2d.csv Light: Measured light at the seabed per day (mol photons m-2 d-1). Figure 3: Fig. 3a.csv Irradiance: Mean irradiance (micro mol photons m-2 s-1). P/R: Productivity/respiration ratios (micro mol photons O2-1 gFW-1 h-1). Figure 3: Fig. 3b.csv Light: Mean irradiance (micro mol photons m-2 s-1) in experimental treatments. Growth: Thallus growth (mm) of Palmaria decipiens under experimental treatments. Figure 3: Fig. 3c.csv Des, Him, Irr, Pal: Ice-free days required for minimum annual light budget Figure 3: Fig. 3c.bars.csv Prop: relative cover (sums to 1 per site) of algae and invertebrates, excluding Inversiula nutrix and Spirorbis nordenskjoldi. Figure 4: Fig. 4.csv Time: months after deployment Length: length of thalli (mm) Figure 5: Fig. 5c and d.csv Axis 1 and Axis 1: Values from first two axes of principal coordinate analysis IceCover: proportion of days that each site is free of sea-ice per year. Beta: Beta-diversity. Calculated as Jaccard similarity between the most ice-covered site (OB1) and each other site. Figure 5: Fig. 5e and f.csv IceCover: proportion of days that each site is free of sea-ice per year. Value: number of species per boulder (for Metric=Diversity), or percent cover per boulder (for Metric=Cover). Figure 6: Fig. 6a.csv Sites.lost: number of sites removed from dataset due to sea-ice loss. Ice: maximum ice-free days within the region (d yr-1). S: Total species richness across each subset of sites. Effort: relative sampling effort (number of sites sampled).

Data are automatically and manually collected from a range of sensors on board Australian Antarctic Program vessels. From the 2021-2022 season onwards, this typically means the RSV Nuyina. The RSV Nuyina presently has approximately 90 instruments available to produce data. The instruments that contribute data to a specific dataset can be found in that voyages instrument coverage document. In addition the data from the instruments, the RSV Nuyina can also record data from spaces on the ship such as the containerised laboratories or the Wet Well. The RSV Nuyina also has a science tender which includes four instruments as well. Previous datasets from the Aurora Australis generally comprised only "underway data" - such as weather data, water temperatures, and so on. Data from the Nuyina are much broader in scope and more detailed. For full details for each dataset, see the associated child record. Oceanographic instruments that typically record data continuously throughout RSV Nuyina voyages include the Eco fluorometer, LISST-200X particle size analyser, Phytoflash flurometer, SeaFET pH sensor, SBE38 thermometer, SBE45 thermosalinograph, SBE63 oxygen sensor and the PC02 system. Oceanographic and mapping instruments that typically record data intermittently throughout voyages include the ADCP38, ADCP150, EK80 hull system, EK80 dropkeel system, Hydrophones dropkeel system, MS70 fisheries sonar, Multibeam EM712, Multibeam EM122, TOPAS sub-bottom profiler, SH90 fish finding sonar, sound velocity sensors, Ice Wave Radar and the ISAR infrared sea surface temperature system. Meteorological instruments that typically record data continuously throughout voyages include the WMT700 ultrasonic anemometers, UVB radiometer, CGR3 pyrgeometer, CMP3 global solar radiometer, CUV5 broadband UV radiometer, PQS1 photosynthetically active radiometer, CL31 Ceilometer, HMP155 air temperature and humidity sensor, PWD22 present weather and visibility sensor, PTB330 digital barometer and the all sky imager. Deployable instruments that typically record data intermittently throughout voyages include the XBT, RBR concerto CTD, sound velocity profiler, NUTTS instruments and CTD instruments. Operational and positioning instruments that record data continuously throughout voyages include the Gyro compass, GPS compass, IPMS alarm system and webcams. Operational and positioning instruments that record data intermittently throughout voyages include the winches, USBL, Hydrophones hull system, draught sensor, speedlog, echosounder 50 KHz, echosounder 200 KHz, seapath380 systems, acoustic net monitors, Arc-X radar and the hull stress and ice load monitor.

This dataset contains the Voyage Data from Voyage 2 2021-22 collected during RSV Nuyina’s maiden voyage to Antarctica. This purpose of this voyage was a combination of commissioning trials, ice trials and a resupply voyage. The voyage departed Hobart and visited Davis station, Casey station, and the Vanderford Glacier before returning to Hobart. Throughout the voyage, operations related to ice trials and commissioning the science systems were conducted. As the instruments were commissioned, the data produced was included in the Voyage Dataset. It should be noted that many of the instruments were uncalibrated and, therefore, data recorded from these instruments may be erroneous. Oceanographic instruments that recorded data continuously throughout RSV Nuyina voyages include the Eco fluorometer, LISST-200X particle size analyser, Phytoflash flurometer, SeaFET pH sensor, SBE38 thermometer, SBE45 thermosalinograph and the SBE63 oxygen sensor. Oceanographic and mapping instruments that recorded data intermittently throughout the voyage include the ADCP38, ADCP150, EK80 hull system, EK80 dropkeel system, hydrophones dropkeel system, MS70 fisheries sonar, multibeam EM712, multibeam EM122, TOPAS sub-bottom profiler and the sound velocity sensor drop keel system. Meteorological instruments that record data continuously throughout the voyage include the WMT700 ultrasonic anemometers, UVB radiometer, CGR3 pyrgeometer, CMP3 global solar radiometer, CUV5 broadband UV radiometer, PQS1 photosynthetically active radiometer, CL31 Ceilometer, HMP155 air temperature and humidity sensor, PWD22 present weather and visibility sensor, PTB330 digital barometer and the all sky imager. Deployable instruments that recorded data throughout the voyage include the XBT, RBR concerto CTD, sound velocity profiler, NUTTS instruments and CTD instruments. Operational and positioning instruments that recorded data continuously through the voyage include the gyro compass, IPMS alarm system and webcams. Operational and positioning instruments that recorded data intermittently throughout the voyage include the winches, USBL, hydrophones hull system, draught sensor, speedlog, echosounder 50 kHz, echosounder 200 kHz and seapath380 systems. A list of the instruments used on the voyage is available in the file, "instrument_coverage_202122020.pdf" at the top level of the dataset. To find information on the science systems themselves and the headers for the data please refer to "voyage_202122020_data_description.pdf".

This dataset contains the Voyage Data from voyage 202122050 undertaken by the RSV Nuyina between February 12th and March 27th 2022. The principal objectives of the voyage were to retrieve equipment and exchange personnel from Davis Station, and resupply Macquarie Island Station. The EK80 acoustic instruments, underway oceanographic instruments in the OceanPack system, the ice and wave radar, and meteorological instruments were all run during this voyage. Whole of voyage data from the RSV Nuyina underway instruments. Includes uncontaminated seawater, meteorological, and wave radar data interpolated to 1 minute measurements. Wherever possible, each parameter and its associated unit of measurement complies with the NetCDF Climate and Forecast (CF) Metadata Convention Standard Name Table (Version 29) - “voyage_202122050\underway_merger\netcdf\202122050_1min_all.nc