Description: During two cruises wiht RV Sonne, SO234-2 from 8 to 19 July 2014 (Durban, South Africa to Port Louis, Mauritius) and SO235 from 23 July to 7 August 2014 (Port Louis, Mauritius to Malé, Maldives), within the SPACES (Science Partnerships for the Assessment of Complex Earth System Processes) and OASIS (Organic very short-lived Substances and their air sea exchange from the Indian Ocean to the Stratosphere) research projects, surface water samples were sampled from a continuous running pump in the hydrographic shaft of RV Sonne at a depth of 5 m. Deep water samples were taken from a Niskin-bottle rosette sampler. The samples were then analyzed for halogenated compounds using a purge and trap system onboard, which was attached to a gas chromatograph with an electron capture detector for surface water samples and a GC/MS Agilent 5975 for the deep water samples. An analytical reproducibility of 10% was determined from measuring duplicate water samples, detection limit was 0.2 pmol /L. Calibration was performed with several dilutions of a mixed-compound standard prepared in methanol.

Description: Between 1733 and 1895, a total of 35 additional volcanic eruptions were detected in the new high-resolution measurements (D4i dataset: "Greenland ice-core non-sea-salt sulfur concentrations and calculated volcanic sulfate deposition (1733-1900 CE)" (PANGAEA, doi:10.1594/PANGAEA.960977) of the D4 ice core (McConnel et al., 2007). For the same time period only 25 volcanic eruptions had previously been detected using an ice-core array from Greenland (including NEEM-2011-S1 and NGRIP) and Antarctica, making up the eVolv2k database [Toohey and Sigl, 2017]. 21 volcanic events in D4i are found to match events in the eVolv2k database, 8 tropical events and 13 Northern Hemisphere extratropical (NHET) events. Based on linear fits of eVolv2k volcanic stratospheric sulfur injections (VSSI) to the cumulative D4i sulfate deposition rates, we derive scaling factors to convert D4i volcanic sulfate depositions to VSSI. Fits are of high quality with R2 values of 0.91 and 0.99 for tropical and extratropical events, respectively. Of the remaining events identified in D4i but not included in eVolv2k, we find 11 that are tentatively attributable to VEI=4 events listed in the Volcanoes of the World [Global Volcanism Program, 2013] (GVP) database (e.g, Soufriere St. Vincent, and Awu in 1812; Suwanosejima in 1813; Mayon 1814; Raung 1817; Colima 1818). Although attribution is not completely certain, for these events we assume the attribution is correct and use the historically dated eruption date and location from Volcanoes of the World (Global Volcanism Program, 2013). Eruptions found in D4i which do not have a corresponding event in the GVP database could result from a number of scenarios. To avoid a potential bias by attributing these signals to either tropical latitudes (0°) or to NHET latitudes (i.e. 45°N), we represent the forcing by these unidentified events as the probability-weighted superposition of tropical and extratropical eruptions based on the measured sulfate flux. For each event we calculate the VSSI associated with the sulfate deposition assuming on the one hand the event was tropical, and on the other hand assuming it was extratropical. These VSSI values are then multiplied by the probability that the event was either tropical or extratropical, based on the proportion of NHET and tropical events in the Greenland records used in eVolv2k. Each unidentified sulfate deposition is then represented in the VSSI file as two injections, with the same eruption time taken from the ice ice-core dating, and different VSSI amounts for default tropical and extratropical regions. The resulting list of "additional" eruptions not included in eVolv2k is merged with eVolv2k, and the resulting eruption list named eVolv2k plus D4i used as input to the EVA forcing generator [Toohey et al., 2016] to generate time series of stratospheric aerosol optical depth (SAOD).

Description: Based on a set of continuous sulfate records from a suite of ice cores from Greenland and Antarctica, the HolVol v.1.0 database includes estimates of the magnitudes and approximate source latitudes of major volcanic stratospheric sulfur injection (VSSI) events for the Holocene (from 9500 BCE or 11500 year BP to 1900 CE), constituting an extension of the previous record by 7000 years. The database incorporates new-generation ice-core aerosol records with sub-annual temporal resolution and demonstrated sub-decadal dating accuracy and precision. By tightly aligning and stacking the ice-core records on the WD2014 chronology from Antarctica we resolve long-standing previous inconsistencies in the dating of ancient volcanic eruptions that arise from biased (i.e. dated too old) ice-core chronologies over the Holocene for Greenland. A long-term latitudinally and monthly resolved stratospheric aerosol optical depth (SAOD) time series is reconstructed from the HolVol VSSI estimates, representing the first such reconstruction Holocene-scale reconstruction constrained by Greenland and Antarctica ice cores. These new long-term reconstructions of past VSSI and SAOD variability confirm evidence from regional volcanic eruption chronologies (e.g., from Iceland) in showing that the early Holocene (9500-7000 BCE) experienced a higher number of volcanic eruptions (+16%) and cumulative VSSI (+86%) compared to the past 2,500 years. This increase is coinciding with then rapidly retreating ice sheets during deglaciation, providing context for potential future increases of volcanic activity in regions under projected glacier melting in the 21st century.

Description: Assessments of climate sensitivity to projected greenhouse gas concentrations underpin environmental policy decisions, with such assessments often based on model simulations of climate during recent centuries and millennia1, 2, 3. These simulations depend critically on accurate records of past aerosol forcing from global-scale volcanic eruptions, reconstructed from measurements of sulphate deposition in ice cores4, 5, 6. Non-uniform transport and deposition of volcanic fallout mean that multiple records from a wide array of ice cores must be combined to create accurate reconstructions. Here we re-evaluated the record of volcanic sulphate deposition using a much more extensive array of Antarctic ice cores. In our new reconstruction, many additional records have been added and dating of previously published records corrected through precise synchronization to the annually dated West Antarctic Ice Sheet Divide ice core7, improving and extending the record throughout the Common Era. Whereas agreement with existing reconstructions is excellent after 1500, we found a substantially different history of volcanic aerosol deposition before 1500; for example, global aerosol forcing values from some of the largest eruptions (for example, 1257 and 1458) previously were overestimated by 20–30% and others underestimated by 20–50%.

Description: The injection of sulphur into the stratosphere by explosive volcanic eruptions is the cause of significant climate variability. Based on sulphate records from a suite of ice cores from Greenland and Antarctica, the eVolv2k database includes estimates of the magnitudes and approximate source latitudes of major volcanic stratospheric sulphur injection (VSSI) events from 500 BCE to 1900 CE, constituting an update of prior reconstructions and an extension of the record by 1000 years. The VSSI estimates incorporate improvements to the ice core records in terms of synchronization and dating, refinements to the methods used to estimate VSSI from ice core records, and includes first estimates of the random uncertainties in VSSI values. VSSI estimates for many of the largest eruptions, including Samalas (1257), Tambora (1815) and Laki (1783) are within 10% of prior estimates. A number of strong events are included in eVolv2k which are largely underestimated or not included in earlier VSSI reconstructions, including events in 540, 574, 682 and 1108 CE. The long term annual mean VSSI from major volcanic eruptions is estimated to be ∼ 0.5 Tg [S] yr−1, ∼ 50 % greater than a prior reconstruction, due to the identification of more events and an increase in the magnitude of many intermediate events. A long-term, latitudinally and monthly resolved stratospheric aerosol optical depth (SAOD) time series is reconstructed from the eVolv2k VSSI estimates, and the resulting global mean SAOD is found to be similar (within 33%) to a prior reconstruction for most of the largest eruptions. The long-term (500 BCE–900 CE) average global mean SAOD estimated from the eVolv2k VSSI estimates and including a constant "background" injection of stratospheric sulphur is ∼ 0.014, 30 % greater than a prior reconstruction. These new long-term reconstructions of past VSSI and SAOD variability give context to recent volcanic forcing, suggesting that the 20th century was a period of somewhat weaker than average volcanic forcing, with current best estimates of 20th century mean VSSI and SAOD values being 25 and 14 % less, respectively, than the mean of the 500 BCE to 1900 CE period. The reconstructed VSSI and SAOD data are available at https://doi.org/10.1594/WDCC/eVolv2k_v2〉.

Description: The Stratospheric Sulfur and its Role in Climate (SSiRC) interactive stratospheric aerosol model intercomparison project (ISA-MIP) explores uncertainties in the processes that connect volcanic emission of sulphur gas species and the radiative forcing associated with the resulting enhancement of the stratospheric aerosol layer. The central aim of ISA-MIP is to constrain and improve interactive stratospheric aerosol models and reduce uncertainties in the stratospheric aerosol forcing by comparing results of standardized model experiments with a range of observations. In this paper we present 4 co-ordinated inter-model experiments designed to investigate key processes which influence the formation and temporal development of stratospheric aerosol in different time periods of the observational record. The "Background" (BG) experiment will focus on microphysics and transport processes under volcanically quiescent conditions, when the stratospheric aerosol is controlled by the transport of aerosols and their precursors from the troposphere to the stratosphere. The "Transient Aerosol Record" (TAR) experiment will explore the role of small- to moderate-magnitude volcanic eruptions, anthropogenic sulphur emissions and transport processes over the period 1998–2012 and their role in the warming hiatus. Two further experiments will investigate the stratospheric sulphate aerosol evolution after major volcanic eruptions. The "Historical Eruptions SO2 Emission Assessment" (HErSEA) experiment will focus on the uncertainty in the initial emission of recent large-magnitude volcanic eruptions, while the "Pinatubo Emulation in Multiple models" (PoEMS) experiment will provide a comprehensive uncertainty analysis of the radiative forcing from the 1991 Mt. Pinatubo eruption.

Description: The pre-industrial millennium is among the periods selected by the Paleoclimate Model Intercomparison Project (PMIP) for experiments contributing to the sixth phase of the Coupled Model Intercomparison Project (CMIP6) and the fourth phase of the PMIP (PMIP4). The past1000 transient simulations serve to investigate the response to (mainly) natural forcing under background conditions not too different from today, and to discriminate between forced and internally generated variability on interannual to centennial timescales. This paper describes the motivation and the experimental set-ups for the PMIP4-CMIP6 past1000 simulations, and discusses the forcing agents orbital, solar, volcanic, and land use/land cover changes, and variations in greenhouse gas concentrations. The past1000 simulations covering the pre-industrial millennium from 850 Common Era (CE) to 1849 CE have to be complemented by historical simulations (1850 to 2014 CE) following the CMIP6 protocol. The external forcings for the past1000 experiments have been adapted to provide a seamless transition across these time periods. Protocols for the past1000 simulations have been divided into three tiers. A default forcing data set has been defined for the Tier 1 (the CMIP6 past1000) experiment. However, the PMIP community has maintained the flexibility to conduct coordinated sensitivity experiments to explore uncertainty in forcing reconstructions as well as parameter uncertainty in dedicated Tier 2 simulations. Additional experiments (Tier 3) are defined to foster collaborative model experiments focusing on the early instrumental period and to extend the temporal range and the scope of the simulations. This paper outlines current and future research foci and common analyses for collaborative work between the PMIP and the observational communities (reconstructions, instrumental data).