Marine Biological Productivity Research Articles

Unravelling changes in the productivity regime during the Late Miocene-Early Pliocene Biogenic Bloom: Insights from the western equatorial Pacific (IODP Site U1488)

The Late Miocene-Early Pliocene Biogenic Bloom (9.0–3.5 Ma) is a widespread paleoceanographic phenomenon marked by increased marine biological productivity and by high accumulations of biological components documented at multiple open ocean sites in the Indian, Pacific, and Atlantic oceans. We investigate the expression of the Biogenic Bloom at International Ocean Discovery Program (IODP) Site U1488 in the western equatorial Pacific Ocean. We generated an improved age model based on calcareous nannofossil biostratigraphy and a quantitative benthic foraminiferal record across the Late Miocene to the Early Pliocene. Increased carbonate mass accumulation rates suggest the Biogenic Bloom occurs between 8.1 and 4.0 Ma at Site U1488. We described four intervals with paleoenvironmental significance: Interval 1 (8.1–6.2 Ma), Interval 2 (6.2–5.5 Ma), Interval 3 (5.5–4.5 Ma), and Interval 4 (4.5–3.1 Ma), the Biogenic Bloom spans across Interval 1 and 3. Intervals 1, 3, and 4 are marked by high abundance of phytodetritus exploiting taxa, related to phases of El Niño-like conditions. The highest abundance of these species during Interval 1 has been related to a phase of higher seasonality. In contrast, intervals 3 and 4 show reduced seasonality and a steadier input of food to the seafloor, associated with increased dust supply through wind transport and/or increased continental weathering during the Pliocene. Interval 2 stands out as the sole interval encompassing La Niña-like conditions, marked by a shift in the nutrient composition reaching the seafloor, from labile phytodetritus to refractory organic matter, and possibly a decrease in seasonality.

Impacts of glacial discharge on the primary production in a Greenlandic fjord

Subglacial discharge from marine-terminating glaciers in Greenland injects large volumes of freshwater and suspended sediment into adjacent fjord environments. Although the discharge itself is nutrient poor, the formation of meltwater plumes can enhance marine biological production by stimulating upwelling of nutrient-rich fjord water. Despite the importance of meltwater discharge to marine ecosystems, little is known of the quantitative impact of discharge processes on phytoplankton growth, including the effects of local plumes, fjord-wide stirring and mixing, and suspended sediments on net primary production (NPP). Here, we report simulations of Bowdoin Fjord in northwestern Greenland using coupled non-hydrostatic ocean circulation and lower-trophic level ecosystem models, developed using field data. Our findings demonstrate that subglacial discharge plays a crucial role in NPP by stirring and mixing the entire fjord water system, which has a greater effect on NPP than local plume upwelling. Sensitivity tests suggest a 20% increase in NPP under conditions of enhanced discharge anticipated in the future. However, if glacier discharge and retreat exceed critical levels, NPP is predicted to decline by 88% relative to present values. This pattern reflects the negative impact of increased sediment flux on photosynthesis and weakened fjord stirring and mixing resulting from shallower outlet depths.

Ocean bottom-water oxygenation across the Late Miocene–Early Pliocene biogenic bloom

The Late Miocene–Early Pliocene biogenic bloom (ca. 9–3.5 millions of years ago, My) represents a period of globally heightened marine biological productivity. Paleoenvironmental studies across this interval show alternating phases of low-oxygen eutrophic and well-oxygenated oligotrophic conditions. Here, we focus on the bottom water oxygenation changes during the biogenic bloom to assess the validity of the enhanced Benthic Foraminifera Oxygen Index (EBFOI). The index was calculated for three ocean drilling sites: Ocean Drilling Program Site 1085 (southeast Atlantic), and International Ocean Discovery Program sites U1506 (southwest Pacific) and U1488 (equatorial Pacific). The quantitative study of benthic foraminiferal assemblages from Site 1488 allowed us to infer the paleoenvironmental evolution across the biogenic bloom. At this site, we document a shift from stable oxygen concentrations and seasonal input of phytodetritus (8.7–4.3 My) to short-term fluctuations between low oxygen eutrophic conditions and well-oxygenated oligotrophic conditions (4.3–3.0 My). The EBFOI calculated at sites 1085 and U1506 was cross-referenced with the published paleoenvironmental conditions. While the EBFOI proves to be a valuable tool to infer paleoenvironmental changes at the seafloor, it has limitations, as evidenced by comparisons with paleoenvironmental interpretations of Site U1488, where it does not consistently align with inferred oxygen conditions.

Speciation patterns of zinc in ocean particles.

Different particulate zinc forms ultimately affect marine biological productivity.

Late Pleistocene-Holocene sea level and climate changes in the Gulf of Saros: Evidence from seismostratigraphic record and sediment core data

A detailed record of sea level changes and climate oscillations in the Gulf of Saros during the late Pleistocene to the Holocene is provided by high-resolution seismic reflection profiles and analysis of a sediment core. The seismic stratigraphy reveals the formation of four main depositional units bounded by prominent reflection surfaces, reflecting high sea level variations. The Last Glacial Maximum period in the gulf is associated with the lowstand sea level, forming the deepest marine terrace at −148 m. The increasing sea level due to post-glacial warming was accompanied by the deposition of transgressive units characterized by coastal onlaps together with local channel-fills. This transgressive phase was modulated by three brief still-stands sea levels at 17 cal ka BP, 14.6 cal ka BP and 13.6 cal ka BP, producing the younger marine terraces in the gulf at −135 m, −112 m and −90 m, respectively. A comparison of their depths with the global sea level curve reveals elevation differences with decreasing subsidence rates from the older to younger ages, implying tectonic subsidence along the gulf floor.The close correlation of multi-proxy data from core SAG-22 in the gulf with the northern Aegean and Anatolia data strongly indicates that the timings of the past climate events generally agree with the global and regional climate patterns. The warm climate around the gulf during the late phase of Bølling/Allerød (13.3–12.6 cal ka BP) is represented by high marine biological productivity and improved ventilation in the deeper water due to subsequent transgression. Permafrost formation in the catchment area during the following cold and dry Younger Dryas period (12.6–11.7 cal ka BP) resulted in reduced soil erosion and sediment input to the gulf. Noticeable warming during the Early Holocene between 11.2 cal ka BP and 9.4 cal ka BP is recorded by the multi-proxy data of the core when the enhanced marine biological productivity occurred above the poorly oxygenated deep water column. The climatic deterioration to a cooler and drier phase during the Early to Middle Holocene transition (9.4–7.8 cal ka BP) resulted in intense physical weathering and erosion, causing the highest sedimentation in the gulf. The later period of the Holocene is associated with the formation of two discrete sapropels at 7.8 cal ka BP and 5.4 cal ka BP that were accompanied by warm and wet climates around the gulf.

A benthic foraminifera perspective of the Late Miocene-Early Pliocene Biogenic Bloom at ODP Site 1085 (Southeast Atlantic Ocean)

The Late Miocene-Early Pliocene Biogenic Bloom (ca. 9.0–3.5 Ma) was a phase of high marine biological productivity documented globally at multiple ocean sites, related to an increase in nutrient input and/or a significant reorganization of nutrients in the oceans. Here, we studied the Biogenic Bloom at Ocean Drilling Program (ODP) Site 1085 in the Southeast Atlantic Ocean, additionally providing an updated age model based on calcareous nannofossil biostratigraphy. During the event, we identified four intervals characterised by distinct benthic foraminiferal assemblages, suggesting changes in paleoenvironmental/paleoceanographic conditions. The Biogenic Bloom extends from 8.1 to 3.0 Ma at Site 1085, as detected by different proxies such as linear sedimentation rates, carbonate mass accumulation rates, benthic foraminiferal indices and assemblage data. The inferred paleoenvironmental changes allowed us to differentiate four intervals within the Biogenic Bloom. From 8.1 to 5.2 Ma and from 3.8 to 3.0 Ma, the high benthic foraminiferal accumulation rates (BFARs) and the abundance of phytodetritus-exploiting taxa point to highly seasonal phytoplankton blooms. Between 5.2 and 4.8 Ma, we document short-term fluctuations between well‑oxygenated conditions with transient input of phytodetritus and phases of low oxygen eutrophic conditions. Between 4.8 and 3.8 Ma, a decrease in opportunistic species and an increase in eutrophic taxa likely suggest a switch to a higher food supply to the seafloor. Our data shows that the onset of the Biogenic Bloom was synchronous with other global well-dated records and its end appears to align with other Atlantic records. Lastly, our findings support the hypothesis that the Biogenic Bloom was not a single productivity event, but a complex event made up of several short-lived, high-productivity regimes with different driving forces.

Thorium isotope evidence for glacial–interglacial dust storminess and productivity in the North Pacific gyre

The flux of dust deposition to the ocean and its impact on marine biological productivity are outstanding issues of the Earth’s climate system. The North Pacific gyre (NPG) is the Earth’s largest ecosystem and is important for marine nitrogen fixation, which is sensitive to Asian dust-regulated surface nutrient stoichiometry. Meanwhile, it is one of the least studied regions in the global ocean during the late Pleistocene, because of the extremely slow sediment accumulation and lack of biological material preservation. 232Th and 230Th concentrations recorded by hydrogenetic ferromanganese crusts in the deep NPG provide a novel and quantitative proxy of dust deposition and export productivity in this region. For this purpose, we have established an in situ U–Th isotope analytical technique on hydrogenetic ferromanganese crusts collected from the deep NPG. Iron, Mn, and Co of our samples have also been analyzed to constrain the impact of dust dissolution on the Fe geochemical cycle. Remarkably, variability of the 232Th-based dust flux over the last ∼900 ky exhibits a striking resemblance to grain-size records of the Chinese loess deposits and sea-level reconstructions but clearly decouples from the global temperature evolution. On orbital time scales, dust storms over the NPG are apparently sensitive to effects related to continental ice sheet sizes but decoupled from major global cooling during the early glaciation. While our 232Th data indicate a 2- to 3-fold variability of glacial–interglacial dust flux, scavenging of Fe, Mn, and Co in the deep NPG is much less variable through the late Pleistocene. We suggest that variable dust fluxes have a limited impact on the inventory of dissolved Fe in the deep waters of NPG, even though the scavenging of Fe has likely been regulated by glacial–interglacial paleoceanography. The paired 230Th-scavenging-based biological productivity tracks gyre sea surface temperature rather than dust flux during the last glacial cycle. We observe no correlation between dust flux and export productivity in the NPG, indicating that dust-derived Fe is not the productivity-limiting factor on orbital time scales in this region. Instead, these results imply that changes in gyre mixing and mode water formation might have led to increased supply of phosphorous and thus enhanced glacial biological carbon sequestration, with potentially stronger nitrogen fixation under higher eolian input.

Origin of dissolved organic carbon under phosphorus-limited coastal-bay conditions revealed by fluorescent dissolved organic matter

To determine the origins of dissolved organic carbon (DOC) in a bay of volcanic Jeju Island, where the discharge of fresh groundwater (FGW) is dominant, we measured fluorescent dissolved organic matter (FDOM) and implemented a parallel factor analysis (PARAFAC). The PARAFAC model identified three humic-like components (FDOMH) and one protein-like component (FDOMP). DOC was extremely deficient in the FGW (35 ± 13 μM) and positively correlated with salinity in the coastal environment, indicating oceanic DOC contribution. The FDOMP pattern was similar to that of DOC, suggesting that marine biological production is a primary DOC source in this region. Particularly, significant FDOMP correlations in the coastal waters with the fluxes of dissolved inorganic phosphorus (DIP; R2 = 0.31) and dissolved silicon (R2 = 0.46) from the FGW demonstrated that in situ biological production is facilitated by FGW-borne nutrient addition. However, the absence of a correlation between the fluxes of dissolved inorganic nitrogen (DIN) and FDOMP (R2 <0.01) indicated that anthropogenic DIN is not essential for DOC production under the P-limited nutrient conditions and diatom-dominant conditions prevailing on the coastal Jeju Island. Here, we calculated the potential capacity of carbon fixation by marine biological activity based on the Redfield ratio of carbon and phosphorus with DIP fluxes. The flux accounts for approximately 2% of the terrestrial carbon uptake in South Korea. Therefore, optical properties of FDOM may be good indicators of coastal DOC origin, and nutrient speciation may be linked to the carbon cycle.

Role of terrestrial versus marine sources of humic dissolved organic matter on the behaviors of trace elements in seawater

We investigated the behaviors of dissolved trace elements (Mn, Fe, Ni, Cu, Zn, and Cd) associated with humic dissolved organic matter (DOMH) of varying origins in the surface waters of two Korean coastal regions (Jinhae Bay [JH] and offshore Tongyeong [TY]). Both regions displayed intensive scavenging and settling of the particle-reactive Ce and 234Th tracers. However, in JH, where DOMH is mainly terrestrial-derived, the concentrations of trace elements (Fe, Ni, and Cu) were negatively correlated with salinity and positively correlated with DOMH. This indicates that terrestrial DOMH could form complexes with dissolved trace elements, and this complexation likely deters the adsorptive removal of trace elements by settling particles. Similar interactions between trace elements (Mn, Fe, and Cu) and DOMH were also discovered in TY, where most DOMH originated from marine biological production. Our study reveals that both terrestrial and marine DOMH would complex with dissolved trace elements, stabilizing them in the dissolved phase in coastal waters. Therefore, DOMH-trace element complexation in coastal waters could play a key role in regulating the cycling and transport of trace elements in the ocean.

History of Anvers-Hugo Trough, western Antarctic Peninsula shelf, since the Last Glacial Maximum. Part II: Palaeo-productivity and palaeoceanographic changes during the Last Glacial Transition

Following the Last Glacial Maximum (LGM; ca. 23-19 calibrated [cal.] kyr before present [BP]), atmospheric and oceanic warming, together with global sea-level rise, drove widespread deglaciation of the Antarctic Ice Sheet, increasing the flux of freshwater to the ocean and leading to substantial changes in marine biological productivity. On the Antarctic continental shelf, periods of elevated biological productivity, often preserved in the sediment record as laminated (and sometimes varved) diatomaceous oozes (LDO), have been reported from several locations and are typically associated with the formation of calving bay re-entrants during ice sheet retreat. Understanding what drives the formation and deposition of LDOs, and the impact of deglacial processes on biogenic productivity more generally, can help inform how Antarctic coastal environments will respond to current and future ice sheet melting. In this study we utilise a suite of sediment cores recovered from Anvers-Hugo Trough (AHT), western Antarctic Peninsula shelf, which documents the transition from subglacial to glacimarine conditions following retreat of an expanded ice stream after the LGM. We present quantitative absolute diatom abundance (ADA) and species assemblage data, to investigate changes in biological productivity during the Last Glacial Transition (19-11 cal kyr BP). In combination with radiocarbon dating, we show that seasonally open marine conditions were established on the mid-shelf by 13.6 cal kyr BP, but LDOs did not start to accumulate until ∼11.5 cal kyr BP. The ∼1.4 kyr delay between the onset of seasonally open marine conditions and LDO deposition indicates that physiographic changes, and specifically the establishment of a calving bay in AHT, is insufficient to explain LDO deposition alone. LDO deposition in AHT coincides with the early Holocene climatic optimum (∼11.5 – 9.0 kyr) and is therefore explained in terms of increased atmospheric/ocean temperatures, high rates of sea and glacial ice melt and the formation of a well-stratified water column in the austral spring. An implication of our study is that extensive bathymetric mapping in conjunction with detailed core analyses is required to reliably infer environmental controls on LDO deposition.

Annual cycle observations of aerosols capable of ice formation in central Arctic clouds

The Arctic is warming faster than anywhere else on Earth, prompting glacial melt, permafrost thaw, and sea ice decline. These severe consequences induce feedbacks that contribute to amplified warming, affecting weather and climate globally. Aerosols and clouds play a critical role in regulating radiation reaching the Arctic surface. However, the magnitude of their effects is not adequately quantified, especially in the central Arctic where they impact the energy balance over the sea ice. Specifically, aerosols called ice nucleating particles (INPs) remain understudied yet are necessary for cloud ice production and subsequent changes in cloud lifetime, radiative effects, and precipitation. Here, we report observations of INPs in the central Arctic over a full year, spanning the entire sea ice growth and decline cycle. Further, these observations are size-resolved, affording valuable information on INP sources. Our results reveal a strong seasonality of INPs, with lower concentrations in the winter and spring controlled by transport from lower latitudes, to enhanced concentrations of INPs during the summer melt, likely from marine biological production in local open waters. This comprehensive characterization of INPs will ultimately help inform cloud parameterizations in models of all scales.

The Enzymology of Ocean Global Change.

A small subset of marine microbial enzymes and surface transporters have a disproportionately important influence on the cycling of carbon and nutrients in the global ocean. As a result, they largely determine marine biological productivity and have been the focus of considerable research attention from microbial oceanographers. Like all biological catalysts, the activity of these keystone biomolecules is subject to control by temperature and pH, leaving the crucial ecosystem functions they support potentially vulnerable to anthropogenic environmental change. We summarize and discuss both consensus and conflicting evidence on the effects of sea surface warming and ocean acidification for five of these critical enzymes [carbonic anhydrase, ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO), nitrogenase, nitrate reductase, and ammonia monooxygenase] and one important transporter (proteorhodopsin). Finally, we forecast how the responses of these few but essential biocatalysts to ongoing global change processes may ultimately help to shape the microbial communities and biogeochemical cycles of the future greenhouse ocean.

Shipboard observations of atmospheric oxygen in the Southern Ocean during the 2017–2018 austral summer

An in situ measurement system was developed for continuous observations of the mole fractions of atmospheric oxygen (defined as δ(O2/N2)) and carbon dioxide (CO2) and the continuous observation was conducted onboard the research vessel SHIRASE 5003 during its voyage between Australia and Syowa Station, Antarctica, in 2017–2018. The CO2 variation was low with respect to that of δ(O2/N2) in the Southern Ocean, suggesting that the land biospheric and fossil-fuel derived CO2 and O2 emissions negligibly influenced the observations. Therefore, the observed significant variations in the atmospheric O2/N2 can be attributed to the atmosphere-ocean gas exchange. During the southbound voyage in December 2017, we observed large spatial variations in δ(O2/N2) due to marine biological production on the western side of the cruise track. Oceanic O2 fluxes based on a simple model and atmospheric δ(O2/N2) variability were consistent with past oceanic observations. No clear longitudinal gradient in δ(O2/N2) was observed at latitudes toward south of 60° S in December 2017 and February–March 2018. However, local δ(O2/N2) maxima were observed in regions with active marine biological production in December 2017. These observations indicate that local O2 fluxes can also modify the spatial distribution of atmospheric δ(O2/N2) in the Southern Ocean.

Climatically Modulated Dust Inputs from New Zealand to the Southwest Pacific Sector of the Southern Ocean Over the Last 410 kyr

AbstractEolian mineral dust is an active agent in the global climate system. It affects planetary albedo and can influence marine biological productivity and ocean‐atmosphere carbon dynamics. This makes the understanding of the global dust cycle crucial for constraining the dust/climate relationship, which requires long‐term dust emission records for all major dust sources. Despite their importance, the sources of atmospheric dust deposited in the Southern Ocean remain poorly constrained. Eolian dust in the Pacific sector of the Southern Ocean is generally assumed to originate from Australia, with minor contributions from New Zealand. Here, we present a high‐resolution elemental record of terrestrial inputs for the past ∼410 kyr from marine sediment core PS75/100‐4 recovered from east of South Island, New Zealand. Sediment grain size is slightly finer than that of loess deposits from South Island, New Zealand, and is coarser than that of marine sediments in the Tasman Sea to the west of New Zealand, which indicates that the dust originated mainly from New Zealand and not only from Australia. Core PS75/100‐4 records lithogenic mass accumulation rates ranging from ∼0.01 to 0.69 g/cm2/kyr (∼0.20 g/cm2/kyr average), with variations over a factor of ∼3–4 over glacial versus interglacial timescales for the past 410 kyr. Our geochemical data correlate well with the Southern Ocean and Antarctic eolian dust records and suggest a westerly wind‐supplied dust signal from New Zealand. Our findings, therefore, suggest that New Zealand should be considered an important long‐term regional dust source in global dust cycle models.

A potential feedback loop underlying glacial-interglacial cycles

The sawtooth-patterned glacial-interglacial cycles in the Earth’s atmospheric temperature are a well-known, though poorly understood phenomenon. Pinpointing the relevant mechanisms behind these cycles will not only provide insights into past climate dynamics, but also help predict possible future responses of the Earth system to changing CO_2 levels. Previous work on this phenomenon suggests that the most important underlying mechanisms are interactions between marine biological production, ocean circulation, temperature and dust. So far, interaction directions (i.e., what causes what) have remained elusive. In this paper, we apply Convergent Cross-Mapping (CCM) to analyze paleoclimatic and paleoceanographic records to elucidate which mechanisms proposed in the literature play an important role in glacial-interglacial cycles, and to test the directionality of interactions. We find causal links between ocean ventilation, biological productivity, benthic delta ^{18}O and dust, consistent with some but not all of the mechanisms proposed in the literature. Most importantly, we find evidence for a potential feedback loop from ocean ventilation to biological productivity to climate back to ocean ventilation. Here, we propose the hypothesis that this feedback loop of connected mechanisms could be the main driver for the glacial-interglacial cycles.

Concerted measurements of free amino acids at the Cabo Verde islands: high enrichments in submicron sea spray aerosol particles and cloud droplets

Abstract. Measurements of free amino acids (FAAs) in the marine environment to elucidate their transfer from the ocean into the atmosphere, to marine aerosol particles and to clouds, were performed at the MarParCloud (marine biological production, organic aerosol particles and marine clouds: a process chain) campaign at the Cabo Verde islands in autumn 2017. According to physical and chemical specifications such as the behavior of air masses, particulate MSA concentrations and MSA∕sulfate ratios, as well as particulate mass concentrations of dust tracers, aerosol particles predominantly of marine origin with low to medium dust influences were observed. FAAs were investigated in different compartments: they were examined in two types of seawater underlying water (ULW) and in the sea surface microlayer (SML), as well as in ambient marine size-segregated aerosol particle samples at two heights (ground height based at the Cape Verde Atmospheric Observatory, CVAO, and at 744 m height on Mt. Verde) and in cloud water using concerted measurements. The ∑FAA concentration in the SML varied between 0.13 and 3.64 µmol L−1, whereas it was between 0.01 and 1.10 µmol L−1 in the ULW; also, a strong enrichment of ∑FAA (EFSML: 1.1–298.4, average of 57.2) was found in the SML. In the submicron (0.05–1.2 µm) aerosol particles at the CVAO, the composition of FAAs was more complex, and higher atmospheric concentrations of ∑FAA (up to 6.3 ng m−3) compared to the supermicron (1.2–10 µm) aerosol particles (maximum of 0.5 ng m−3) were observed. The total ∑FAA concentration (PM10) was between 1.8 and 6.8 ng m−3 and tended to increase during the campaign. Averaged ∑FAA concentrations in the aerosol particles on Mt. Verde were lower (submicron: 1.5 ng m−3; supermicron: 1.2 ng m−3) compared to the CVAO. A similar contribution percentage of ∑FAA to dissolved organic carbon (DOC) in the seawater (up to 7.6 %) and to water-soluble organic carbon (WSOC) in the submicron aerosol particles (up to 5.3 %) indicated a related transfer process of FAAs and DOC in the marine environment. Considering solely ocean–atmosphere transfer and neglecting atmospheric processing, high FAA enrichment factors were found in both aerosol particles in the submicron range (EFaer(∑FAA): 2×103–6×103) and medium enrichment factors in the supermicron range (EFaer(∑FAA): 1×101–3×101). In addition, indications for a biogenic FAA formation were observed. Furthermore, one striking finding was the high and varying FAA cloud water concentration (11.2–489.9 ng m−3), as well as enrichments (EFCW: 4×103 and 1×104 compared to the SML and ULW, respectively), which were reported here for the first time. The abundance of inorganic marine tracers (sodium, methanesulfonic acid) in cloud water suggests an influence of oceanic sources on marine clouds. Finally, the varying composition of the FAAs in the different matrices shows that their abundance and ocean–atmosphere transfer are influenced by additional biotic and abiotic formation and degradation processes. Simple physicochemical parameters (e.g., surface activity) are not sufficient to describe the concentration and enrichments of the FAAs in the marine environment. For a precise representation in organic matter (OM) transfer models, further studies are needed to unravel their drivers and understand their composition.

Marine productivity and synoptic meteorology drive summer-time variability in Southern Ocean aerosols

Abstract. Cloud–radiation interactions over the Southern Ocean are not well constrained in climate models, in part due to uncertainties in the sources, concentrations, and cloud-forming potential of aerosol in this region. To date, most studies in this region have reported measurements from fixed terrestrial stations or a limited set of instrumentation and often present findings as broad seasonal or latitudinal trends. Here, we present an extensive set of aerosol and meteorological observations obtained during an austral summer cruise across the full width of the Southern Ocean south of Australia. Three episodes of continental-influenced air masses were identified, including an apparent transition between the Ferrel atmospheric cell and the polar cell at approximately 64∘ S, and accompanied by the highest median cloud condensation nuclei (CCN) concentrations, at 252 cm−3. During the other two episodes, synoptic-scale weather patterns diverted air masses across distances greater than 1000 km from the Australian and Antarctic coastlines, respectively, indicating that a large proportion of the Southern Ocean may be periodically influenced by continental air masses. In all three cases, a highly cloud-active accumulation mode dominated the size distribution, with up to 93 % of the total number concentration activating as CCN. Frequent cyclonic weather conditions were observed at high latitudes and the associated strong wind speeds led to predictions of high concentrations of sea spray aerosol. However, these modelled concentrations were not achieved due to increased aerosol scavenging rates from precipitation and convective transport into the free troposphere, which decoupled the air mass from the sea spray flux at the ocean surface. CCN concentrations were more strongly impacted by high concentrations of large-diameter Aitken mode aerosol in air masses which passed over regions of elevated marine biological productivity, potentially contributing up to 56 % of the cloud condensation nuclei concentration. Weather systems were vital for aerosol growth in biologically influenced air masses and in their absence ultrafine aerosol diameters were less than 30 nm. These results demonstrate that air mass meteorological history must be considered when modelling sea spray concentrations and highlight the potential importance of sub-grid-scale variability when modelling atmospheric conditions in the remote Southern Ocean.

Marine organic matter in the remote environment of the Cape Verde islands – an introduction and overview to the MarParCloud campaign

Abstract. The project MarParCloud (Marine biological production, organic aerosol Particles and marine Clouds: a process chain) aims to improve our understanding of the genesis, modification and impact of marine organic matter (OM) from its biological production, to its export to marine aerosol particles and, finally, to its ability to act as ice-nucleating particles (INPs) and cloud condensation nuclei (CCN). A field campaign at the Cape Verde Atmospheric Observatory (CVAO) in the tropics in September–October 2017 formed the core of this project that was jointly performed with the project MARSU (MARine atmospheric Science Unravelled). A suite of chemical, physical, biological and meteorological techniques was applied, and comprehensive measurements of bulk water, the sea surface microlayer (SML), cloud water and ambient aerosol particles collected at a ground-based and a mountain station took place. Key variables comprised the chemical characterization of the atmospherically relevant OM components in the ocean and the atmosphere as well as measurements of INPs and CCN. Moreover, bacterial cell counts, mercury species and trace gases were analyzed. To interpret the results, the measurements were accompanied by various auxiliary parameters such as air mass back-trajectory analysis, vertical atmospheric profile analysis, cloud observations and pigment measurements in seawater. Additional modeling studies supported the experimental analysis. During the campaign, the CVAO exhibited marine air masses with low and partly moderate dust influences. The marine boundary layer was well mixed as indicated by an almost uniform particle number size distribution within the boundary layer. Lipid biomarkers were present in the aerosol particles in typical concentrations of marine background conditions. Accumulation- and coarse-mode particles served as CCN and were efficiently transferred to the cloud water. The ascent of ocean-derived compounds, such as sea salt and sugar-like compounds, to the cloud level, as derived from chemical analysis and atmospheric transfer modeling results, denotes an influence of marine emissions on cloud formation. Organic nitrogen compounds (free amino acids) were enriched by several orders of magnitude in submicron aerosol particles and in cloud water compared to seawater. However, INP measurements also indicated a significant contribution of other non-marine sources to the local INP concentration, as (biologically active) INPs were mainly present in supermicron aerosol particles that are not suggested to undergo strong enrichment during ocean–atmosphere transfer. In addition, the number of CCN at the supersaturation of 0.30 % was about 2.5 times higher during dust periods compared to marine periods. Lipids, sugar-like compounds, UV-absorbing (UV: ultraviolet) humic-like substances and low-molecular-weight neutral components were important organic compounds in the seawater, and highly surface-active lipids were enriched within the SML. The selective enrichment of specific organic compounds in the SML needs to be studied in further detail and implemented in an OM source function for emission modeling to better understand transfer patterns, the mechanisms of marine OM transformation in the atmosphere and the role of additional sources. In summary, when looking at particulate mass, we see oceanic compounds transferred to the atmospheric aerosol and to the cloud level, while from a perspective of particle number concentrations, sea spray aerosol (i.e., primary marine aerosol) contributions to both CCN and INPs are rather limited.

The impacts of land plant evolution on Earth's climate and oxygenation state – An interdisciplinary review

The Paleozoic emergence of terrestrial plants has been linked to a stepwise increase in Earth's O2 levels and a cooling of Earth's climate by drawdown of atmospheric CO2. Vegetation affects the Earth's O2 and CO2 levels in multiple ways, including preferential organic carbon preservation by decay-resistant biopolymers (e.g. lignin) and changing the continental weathering regime that governs oceanic nutrient supply and marine biological production. Over shorter time scales (≤1 Myr), land plant evolution is hypothesized to have occasionally enhanced P weathering and fertilized the oceans, expanding marine anoxia and causing marine extinctions. Oceanic anoxia would eventually become limited by oceanic O2 uptake as oxygen accumulates in the atmosphere and surface oceans when excess organic carbon is buried in marine sediments. Here, we review hypotheses and evidence for how the evolving terrestrial ecosystems impacted atmospheric and oceanic O2 and CO2 from the Ordovician and into the Carboniferous (485–298.9 Ma). Five major ecological stages in the terrestrial realm occurred during the prolonged time interval when land was colonized by plants, animals and fungi, marked by the evolution of 1) non-vascular plants, 2) vascular plants with lignified tissue, 3) plants with shallow roots, 4) arborescent and perennial vegetation with deep and complex root systems, and 5) seed plants. The prediction that land vegetation profoundly impacted the Earth system is justified, although it is still debated how the individual transitions affected the Earth's O2 and CO2 levels. The geological record preserves multiple lines of indirect evidence for environmental transitions that can help us to reconstruct and quantify global controls on Earth's oxygenation and climate state.

Review article: How does glacier discharge affect marine biogeochemistry and primary production in the Arctic?

Abstract. Freshwater discharge from glaciers is increasing across the Arctic in response to anthropogenic climate change, which raises questions about the potential downstream effects in the marine environment. Whilst a combination of long-term monitoring programmes and intensive Arctic field campaigns have improved our knowledge of glacier–ocean interactions in recent years, especially with respect to fjord/ocean circulation, there are extensive knowledge gaps concerning how glaciers affect marine biogeochemistry and productivity. Following two cross-cutting disciplinary International Arctic Science Committee (IASC) workshops addressing the importance of glaciers for the marine ecosystem, here we review the state of the art concerning how freshwater discharge affects the marine environment with a specific focus on marine biogeochemistry and biological productivity. Using a series of Arctic case studies (Nuup Kangerlua/Godthåbsfjord, Kongsfjorden, Kangerluarsuup Sermia/Bowdoin Fjord, Young Sound and Sermilik Fjord), the interconnected effects of freshwater discharge on fjord–shelf exchange, nutrient availability, the carbonate system, the carbon cycle and the microbial food web are investigated. Key findings are that whether the effect of glacier discharge on marine primary production is positive or negative is highly dependent on a combination of factors. These include glacier type (marine- or land-terminating), fjord–glacier geometry and the limiting resource(s) for phytoplankton growth in a specific spatio-temporal region (light, macronutrients or micronutrients). Arctic glacier fjords therefore often exhibit distinct discharge–productivity relationships, and multiple case-studies must be considered in order to understand the net effects of glacier discharge on Arctic marine ecosystems.