Microplastics in Southern Ocean sea ice: a pan-Antarctic perspective

Core collection

The 19 archived sea ice cores used for this study were collected between 2004 and 2022 [Figure 1]. Cores were drilled in austral autumn/winter (March-Aug), spring (Sept-Nov), and late summer season (Dec-Feb) under trace-metal-clean conditions. Of these, 10 cores were first-year pack ice and 9 were first-year landfast ice [Table 1]. Cores drilled during the DML campaign were collected using a Kovacs Mark II corer with an internal diameter of 9 cm, while the rest of the cores were drilled with an electropolished stainless steel corer, suited for trace metal analysis^[31], with an internal diameter of 8 or 14 cm. Ice cores were stored in PE plastic bags for transport and freezer storage and decontaminated for MP analysis, as outlined below.

Laboratory processing

All chemicals and reagents used in this study were pre-filtered over 1.2 µm Whatman GF/C (glass microfiber, 47 mm) filters to mitigate MP contamination from packaging. A Dupont^TM Tyvek full-coverage suit (Bioclean-D non-sterile coverall with hood, manufactured by Cleanroom Garments) was worn during all ice-core cutting and handling in the field, ensuring consistency with the attire used in trace-metal-clean sea ice coring. For laboratory work, 100% cotton clothing was worn as a precaution to minimize contamination from polymer-blend and synthetic textile fibers. Additionally, cotton fibers were excluded from all analyses to further reduce potential contamination. All glassware was pre-rinsed with ethanol and washed in a glassware-only dishwasher, followed by acid rinses with 1% HCl solution. All glassware was covered in aluminum foil to prevent contamination. Nitrile gloves were not worn during the study, except when handling hazardous chemicals, due to evidence suggesting they can contaminate samples and cause false positives^[32]. During each sample transfer step, glassware was thoroughly rinsed with MilliQ^TM water to ensure particles had not adhered to the walls of any containers.

As the ice cores were archived samples, processing occurred across three different institutions: the Norwegian Polar Institute (NPI; Tromsø, Norway), the Institute for Marine and Antarctic Studies (IMAS; Hobart, Tasmania), and the Université Libre des Bruxelles (ULB; Brussels, Belgium). Therefore, ice core handling varied slightly based on laboratory infrastructure. The following is a brief overview of the ice-core processing method used to isolate and identify MPs.

All ice cores were cut with individual consideration for the ice crystal structure and ice algal biomass (chlorophyll a and particulate organic carbon) within the ice. The cutting of the 19 cores resulted in a total of 60 ice-core horizons for processing and analysis. To ensure there was no contamination due to ice-core storage in LDPE bags for transport and storage, the outside of the core (approx. 1-2 mm) was scraped off with a ceramic knife (Kyocera) pre-cleaned with MilliQ^TM water. Core horizons were melted in glass containers at room temperature. Oxidative digestions using 2% sodium dodecyl sulfate (SDS; BDH Laboratory Supplies, England) solution and 35% hydrogen peroxide (H₂O₂; Chem-Supply) were performed over the course of 48 h at 50 °C to reduce biological material in each sample. Next, the treated meltwater was filtered through silica sand (50-70 µm particle size, Sigma-Aldrich) and the filtrate was discarded to waste. Density separations were then performed on the sand mixture (and potentially entrapped MPs) by being placed in a supersaturated NaCl solution (NaCl > 99%, Sigma-Aldrich), stirred for approximately 15 min, and left to settle for about 3 h. NaCl was chosen based on its sufficiency in MP isolation following Quinn et al. (2017), even for denser polymers such as polyvinyl chloride (PVC) and polyethylene terephthalate (PET)^[33]. The supernatant was filtered onto Whatman anodisc aluminum oxide filters (0.2 µm porosity, 25 mm diameter). Each filter was then placed in an oven to dry for 24 h at 50 °C, following an established oxidative digestive protocol shown to have minimal impact on polymers^[34].

Cores processed at NPI (Rekt, Dml2, Dml4, Dml5, Dml6) and ULB (Brussels3, Liege5, Ispol5, Awecs493, Awecs496, Pipers7, Pipers22, Yrs3, Yrs9) were cut in cold rooms; therefore, additional cold gear was necessary. Thin PE gloves were worn over wool gloves. This additional precaution was not found to increase MPs found in blanks at either institution (see next section). Additionally, ULB cores were cut using a powered band saw, and the outside ice layer of each core horizon was removed with the band saw blade.

Blanks and recovery tests

As cores were cut under slightly different circumstances, laboratory blanks were run at all three institutions in triplicate to ensure reliable MP data from our environmental samples. At each institution, blank ice cores were created with ultrapure MilliQ^TM water and cylindrically frozen. They were then processed identically to our real samples, allowing us to identify potential laboratory contamination and avoid polymer overestimation. Noted total MPs in blanks by institution are as follows: one polyurethane (PUR) and one polystyrene (PS) particle at NPI (mean 0.22 ± 0.38 particles·L^-1), one polyamide (PA) and five PP particles at IMAS (mean 0.67 ± 0.67 particles·L^-1), one PUR, one PS, and two PP particles at ULB (mean 0.44 ± 0.38 particles·L^-1). These particle numbers were subtracted from their relevant samples for final calculations and statistical tests.

Three additional blanks, referred to as “spiked blanks”, were prepared for recovery rate testing. These blanks were made by spiking 1 L of MilliQ^TM water with 50 blue PE beads (20-27 μm diameter; 1.08 g·mL^-1) (Cospheric LLC). The recovery samples were processed in the same manner as the previous blanks and environmental samples. The PE beads were identified and counted using a light microscope, and the average recovery rate was determined to be 96 (±3)%. One of the filters was used for micro-Fourier-transform spectroscopy (µFTIR) analysis to verify that the Purency Microplastic Finder (PMF; Purency; version 4.17) accurately detected the beads and corresponded with visual observations.

µFTIR/chemical imaging and data analysis

Data were collected via μFTIR spectroscopy. A Hyperion 3000 microscope attached to a Vertex 70 spectrometer (both Bruker Optics) was used for chemical imaging of all sample filters. Sample analysis was conducted with OPUS 8.7 software (Bruker), using 128 scans for the background and 16 scans for each frame, with an IR microscope objective of ×3.5 magnification. The 64 × 64 FPA detector was selected (no binning), resulting in 64 × 64 spectra per frame (784 × 784 µm²) with a pixel resolution of ~12.25 × 12.25 µm². Each filter was analyzed by combining 16 × 16 FPA frames to create a hyperspectral image containing over 5 million spectra per filter (12.544 × 12.544 mm²).

The collated OPUS data were exported as an ENVI file and particle analysis was conducted with PMF, an automated analysis software for μFTIR imaging. Machine learning is used in conjunction with an integrated spectral library to directly compare OPUS spectral data and the spectra of known polymers. A baseline confidence rate (hit level) of 90% was set for PA to ensure the software could differentiate true PA particles from similar-looking biological spectra, while 60% was set for all remaining polymer types. For each particle categorized as an MP, software-provided particle area was used to calculate the equivalent spherical diameter (ESD) of each MP. Polymer-dependent false-color images were then generated by PMF to map polymer types, sizes, and locations on each sample filter.

To determine whether variables had normal distributions prior to correlation analyses, the Shapiro-Wilk test was conducted. The non-parametric Mann-Whitney-U test was performed to determine if there was a significant difference in median MP abundances by sampling season and ice type, as well as investigating differences in median particle size between pack and fast ice, and across the ice core’s sampling seasons. All tests were performed using the statistical analysis software R (version 4.4.1).

MP abundance in entire sea ice cores

MP contamination was identified in every sampled sea ice core [Figure 2]. In total, 4,090 MP particles were found in this study, averaging a concentration of 44.8 (± 50.8, median = 23.3) particles·L^-1. There was a significant difference in median particle abundance between autumn/winter vs. spring cores (P = 0.038) and autumn/winter vs. summer cores (P = 0.019), though there was no statistical difference found between spring and summer concentrations (P = 0.529).

Figure 2. (A) MP concentrations (particles·L^-1) grouped by season (winter samples colored in blue, spring in green, and summer in red) and ice type (^*denotes landfast ice cores); and (B) presented as the total concentration of MPs per ice core delineated by region: BS, WS, QML, DAV, MS, and RS. MP: Microplastic; BS: Bellinghausen Sea; WS: Weddell Sea; QML: Queen Maud Land; DAV: Davis Station; MS: Mawson Sea; RS: Ross Sea.

Cores collected during austral spring (Brussels3, Liege5, Davis5, Sipex4, Sipex7, Yrs9) and summer (Ispol5, Rekt, Dml2, Dml4, Dml5, Dml6, Casey2, Totten1, Yrs3) reported median MP quantities of 10.1 and 16.4 particles·L^-1, respectively [Figure 2]. These are much lower quantities than those recorded in our winter cores (Awecs493, Awecs496, Pipers7, Pipers22) at 130.6 particles·L^-1. Landfast cores showed a lower median concentration of MPs at 13.4 particles·L^-1, compared to pack ice, which had a median of 35.8 particles·L^-1, though this was not found to be statistically significant (P = 0.133).

Across all 19 cores, we calculate an average integrated MP concentration of 2.2 × 10⁵ (± 2.6 × 10⁵) particles·m^-2 in Antarctic sea ice. Our results do not suggest differences in MP counts between years, with no clear temporal trend or variation based on sampling location. Instead, the time of year appears to be the major driver of MP dynamics in sea ice. Integrated concentrations by seasonality are as follows: 3.3 × 10⁵(± 2.8 × 10⁵) particles·m^-2 in autumn and winter ice, 9.7 × 10⁴ (± 4.3 × 10⁴) particles·m^-2 in spring, and 2.3 × 10⁵(± 3.2 × 10⁵) particles·m^-2 in summer. The median integrated concentration of MPs in pack ice is 1.2 × 10⁵ particles·m^-2, compared with 1.8 × 10⁵ particles·m^-2 in fast ice, though this difference was not statistically significant (P = 0.242).

Polymeric composition

A total of 19 polymer types were identified across all samples (see Table 2 for polymer abbreviations and contributions). Polymer types in pack versus fast ice were largely the same. Polyoxymethylene (POM) (19 particles), silicone (2 particles), and polyphenylsulfone (PPSU) (1 particle) were only noted in fast ice samples, while polyetheretherketone (PEEK) (1 particle) was only found in pack ice; the presence of all other polymers was noted in both ice types. PP and PE consistently dominated across the majority of ice core horizons, with only one exception in which PET was the dominant polymer (Pipers22).

Polymer abundance across pack and fast ice was similar but exhibited a few notable differences. The top ten polymers identified for both ice types were the same (PE, PP, PET, PUR, PAN, PVC, PS, PBT, PA, ABS). Pack ice had slightly higher relative concentrations of all polymers, but most notably PET and PUR, which comprised ≈21% of MPs, compared to ≈11% in fast ice. Compositionally, over 18% of MPs found in fast ice were PAN (350/1,927 particles) compared to 4% in pack ice (88/2,163 particles).

Overall, polymer composition across individually sampled sea ice cores was highly variable. However, when regionally grouped, the relative contribution of each polymer was fairly similar between regions [Figure 3].

Figure 3. Polymer composition by geographic region and by ice type, where n equals the total particle abundance.

Particle size

Over 80% of identified particles were ≤ 1,000 µm² and the average particle area for all polymers was 1,033.73 (± 4,501.83) µm². ESD of particles ranged from 13.0 to 506.6 μm, with a mean ESD of 27.4 (± 23.7) μm. A significant difference in median particle size was found between pack and landfast ice cores (P = 0.0015). The mean particle area of landfast cores was 769.4.0 (± 1,640.7) µm², and a mean ESD of 25.6 (± 18.0) μm. Pack ice exhibited a larger mean particle area of 1,258.5 (± 5,747.6) µm², and a mean ESD of 28.9 (± 27.7) μm. The median particle area by season is as follows: 365.1 µm² in winter cores, 315.1 µm² in spring cores, and 265.2 µm² in summer cores. As such, significant differences were found between the median particle area for autumn/winter vs. summer cores (P = 2.6 × 10^-5) and for spring vs. summer cores (P = 0.002); however, no significant difference in median particle area was found between winter and spring cores (P = 0.366).

We found that, in general, particles increased in abundance with decreasing size [Figure 4], and this remained true for both pack and fast ice. The smallest noted particle size was 121 μm² in area (several different polymers) and constituted over 51% of all identified particles (2,099/4,090). The largest particle found in our samples was a piece of PS with an area of 201,561 μm². In fact, PS had the largest mean area across samples [Table 2].

Figure 4. (A) Relative MP particle size distribution from all analyzed stations (n_p = 4,090). Dark blue bars represent particles by length. Light orange bars represent the geometric mean of particle size based on length and width. Particle lengths and widths were measured using PMF; (B) Polymer size abundance across all sea ice samples shown as ESD on a logarithmic scale. MP: Microplastic; PMF: Purency Microplastic Finder; ESD: equivalent spherical diameter.

Spatial and seasonal variability

The spatial and seasonal presence of MPs in sea ice is variable, as seen in Figure 2. Our analysis indicates that coastal sea ice exhibits lower MP abundances than open ocean sea ice. Ice textures are indicative of sea ice growth history, and could help elucidate the mechanisms of MP incorporation, enrichment, and release, as well as the varying levels of MP contamination across drill sites. Pack ice generally has higher frazil ice contributions compared to landfast ice which is mostly made of columnar ice^[35]. The more turbulent conditions associated with open ocean regions due to strong winds and wave action lend themselves to frazil ice formation^[36], in which randomly shaped ice crystals rise from up to 100 m depth^[37] through the water column in autumn and winter, congealing into slush or pancake ice at the ocean surface. We suspect that MPs may get scavenged by frazil ice crystals as they rise to the sea surface, similar to processes suggested for algae and Fe incorporation^[38-41]. Alternatively, frazil ice crystals may use MPs as condensation nuclei and subsequently rise to the ocean surface^[42], leading to MP incorporation into newly formed ice. It has also been suggested that the number of times an ice crystal encounters a particle will determine how much material gets entrained in sea ice^[43], and that convection of sea ice brines and under-ice water, as well as wave action, contribute to particle entrapment^[44]. In contrast, landfast ice often forms in calmer conditions and exhibits higher inclusions of columnar ice growing at the bottom of an existing ice cover^[45]. The bioaccumulation of MPs by algal growth and associated exopolymeric substances (EPS) in the skeletal layer could explain the incorporation of MPs into columnar ice, as suggested in the case of iron, macronutrients, and ice algae^[39,46-49]. Additionally, some of the landfast cores (Yrs and Dml) consisted of platelet ice, which facilitates further incorporation mechanisms for MPs. Basal melting can occur when glacial ice comes into contact with relatively warmer waters, leading to underlying supercooled seawater, which may create favorable conditions for platelet ice formation, buoyant rise, and accumulation under the adjacent landfast sea ice^[50] along with potential entrapment of any MPs present.

We noted that cores collected in spring and summer had significantly lower MP quantities than in winter. Because samples were not obtained from one site across different seasons, it is difficult to make assumptions about the seasonal MP flux during the sea ice growth/melt cycle. However, ice sampled in late winter/early spring is likely to have the highest levels of MP contamination, as suggested for other sea ice variables such as macronutrients and trace metals^[51-53]. This was true for our study as the autumn and winter cores (Awecs493, Awecs496, Pipers7, Pipers22) exhibited the highest mean MP concentrations of all samples [Figure 2]. Sea ice growth rate is fastest in winter and the ice itself is often more frazil-dominant, which, as discussed above, could result in autumn/winter ice cores having higher incorporation rates of MPs than cores collected later in the year. Additionally, turbulent sea ice growth conditions in winter could help explain why the average MP size was significantly larger in winter cores compared to summer cores. Based on mean particle size results from Chen et al. (2023), larger particles are more easily entrapped in ice, and the fast and tumultuous growth conditions for sea ice in winter might assist with particle incorporation into a growing ice column^[54]. Furthermore, our theory on MP flux in the seasonal ice cover is supported through a deeper look at cores sampled later in the sea ice season. As sea ice melts in spring, ice porosity increases, and brine channels can expand and connect with underlying seawater, where particulate matter such as algae (and suspected MPs) may get released from the ice^[55]. Casey2 and Totten1 from late summer in the eastern Antarctic are a prime example of this. Both cores were collected off Wilkes Land in late December, by which point the ice exhibited highly permeable textures with typical characteristics of decaying ice, such as large brine channels and melt holes^[56]. These two cores were among those with the lowest mean concentrations of MPs. Time series are needed to test these hypotheses. Alternatively, mesocosm experiments could be conducted to simulate both sea ice growth and melt phases (e.g., Geilfus et al., 2019)^[27].

Transport mechanisms

MPs in the Southern Ocean may originate from both local and distant sources. While the ACC is thought to keep the Southern Ocean from accumulating MPs from northern latitudes^[19], it has been suggested that both its surface and sub-surface waters are penetrable to MPs^[13,57]. Passive MP transport is heavily influenced by ocean currents and mixing such as meridional overturning circulation (MOC) and Southern Ocean upwelling. Baroclinic wind instability transports mass to the poles and yields southward eddy advection^[58]. Therefore, MPs in surface waters in mid to low latitudes in the upper cell of the MOC are being drawn down into the Southern Ocean and across the axis of the ACC. We noted higher abundances of MPs in pack ice than fast ice may support the theory that contamination is likely coming from northern latitudes, rather than as a direct result of local and intercoastal activities from research bases or fishing ventures. The presence of MPs in Southern Ocean air samples further indicates that MPs can be transported by diffuse sources^[18,59]. The dominance of smaller MPs across our samples was consistent with other Antarctic MP studies that found MP abundance decreased with increasing size^[12,60]. Concurrently, the majority of MPs are less than 10 µm in length, indicating that atmospheric and oceanic long-range transport may assist in MP accumulation across our sea ice sampling sites^[59,61]. In addition, snow deposition may also play a role in depositing MPs into sea ice as MP fragments and fibers are likely to be incorporated into snow mixtures due to their low particle density and pre-enrichment in materials entrained by winds, as it has been observed on the continent at DML stations and reported elsewhere in the literature^[16,62]. However, small MP sizes could simply indicate that particles - whether they originate from local sources or not - are being mechanically degraded over time via marine consumption^[63] or in highly dynamic atmospheric and oceanic conditions^[61,64] and re-enriched into sea ice and surface waters during subsequent seasons. The abundance of MPs in the autumn/winter cores of the Weddell and Ross Seas could indicate that these large oceanic gyres allow for the accumulation of MP contamination during sea ice formation, rather than their re-dispersal in more open ocean regions. Both these regions are characterized as major areas where northern-sourced deep waters cross the ACC before upwelling southward and toward the surface^[23]. The upwelling of deep waters in the Weddell and Ross gyres is a good source candidate of MPs for the surface waters (hence the pack sea ice) in the Southern Ocean since the highest concentration of MPs is found between 200 and 600 m depth in offshore waters of the World’s ocean (e.g., Choy et al., 2019)^[65]. For example, Isobe et al. (2017) observed higher MP concentrations in surface waters south of the Polar Front than in waters north of it^[12]. This hypothesis is further supported by the significantly higher MP concentration found in offshore waters of the Weddell Gyre (where deep-water upwelling prevails) compared to waters on the Weddell Sea continental shelf by Leistenschneider et al. (2024)^[66]. On the contrary, waters on the Antarctic Shelf may be protected from this MP contamination by the Southern Ocean slope front, just north of the continental slope, which partially protects the continental shelf from the intrusion of deeper waters. Further research on pathways of particle transport in the Southern Ocean and sea ice is needed to garner a deeper understanding of contamination levels, and to accurately predict MP sinks as plastic production continues to increase.

In conjunction with seasonal ice characteristics, sampling locations may also help explain the disparity between volumetric MP concentrations in the autumn/winter cores versus the summer/spring cores. We suspect accumulation trends may result from a combination of faster sea ice growth during autumn/winter (and thus more efficient MP entrapment), proximity to external sources of pollution transported by means of wind, subsurface waters (particularly for neutrally buoyant MPs), and local hydrographic features. An MP accumulation model^[6] showed that the Antarctic was initially reasonably well protected from MPs sourced externally to the Southern Ocean, but at the end of the 50-year time span, MP contamination had heavily penetrated the Southern Ocean and was present around the entire Antarctic coastline, with MP abundance remaining most dense in Pacific Ocean sectors during winter. This corresponds with our findings, as Pipers7 and Pipers22 sampled during winter near the Ross Sea^[67] accounted for the highest particle abundances across all our cores (163.1 and 153.8 particles·L^-1, respectively). The remaining cores collected during the sea ice growth phase in the Weddell Sea (Awecs493 and Awecs496)^[68] also exhibited higher MP concentrations than any spring/summer cores. As the model progressed, the region with the highest winter accumulation was the Bellinghausen Sea. Brussels3 and Liege5 were drilled during austral spring in this region and maintained significantly higher MP abundances than any other spring/summer cores (average of 98.4 and 31.1 particles·L^-1, respectively). Researchers noted that sea ice permeability was significantly reduced for Brussels3 in particular, which could explain the high concentration of particles within this core^[69], despite cycles of warming beginning in early spring, thus retaining MPs that were enriched during winter. In contrast, cores drilled in East Antarctica during the sea ice melt phase (Davis5, Sipex4, Sipex7, Casey2, Totten1) exhibited the lowest mean concentrations of MPs among all samples. This could be because the largest hydrological features in the eastern Antarctic remain the ACC and the Antarctic Coastal Current, and the region lacks a large gyre system that can potentially entrap MPs. Simultaneously, we speculate that this could be a result of low vessel traffic, and greater distance from tourist and research hotspots. Cunningham et al. (2022) demonstrated that air masses and wind are transport mechanisms for MP entering the Southern Ocean and noted that MPs in their study were likely to have originated from South America^[18], which would likely be the case for some of our Weddell Sea ice cores. Perhaps because the eastern Antarctic is further removed from the southern land masses of Africa and South America, airborne MP pollution is not as significant of a factor. This, coupled with the lower rates of tourism and marine activities, could explain the lower MP counts in these cores.

Potential sources for MPs in sea ice

We suspect MP particles are scavenged from surrounding environmental media and incorporated into the sea ice matrix during its growth phase. Based on comparisons with MP studies in surface and subsurface waters, sea ice is a temporary sink for MPs. The mean concentrations of particles·L^-1 across our cores were consistently four to six orders of magnitude higher than concentrations in seawater [Table 3]. Note that at the time of the current study, there are no comparable reports of MP concentrations in the Bellinghausen or Mawson Seas. In general, the lack of standardized methods for MP extraction from seawater and chemical identification remains a hindrance to consistent cross-study comparisons. Additionally, most studies in the Antarctic are focused on regions with long-standing research stations or those experiencing higher levels of anthropogenic pressures. As such, there have been mixed reports of MP presence in Antarctic surface waters, with some studies finding high levels of MPs in offshore surface waters^[19] while others reporting little to no presence of MPs at all^[7,73]. Thus, MP incorporation during initial sea ice growth may coincide with the higher abundances of MPs we noted in our autumn/ winter cores compared to those sampled during spring and summer. It may also account for why studies reporting contamination continually note MPs in Antarctic sub-surface waters^[60] and sediments^[17,74] but vary widely in their findings for upper-surface waters in both coastal and offshore regions.

Air masses may also contribute MPs in sea ice. To date, little remains known about the presence of airborne MPs in Antarctica, though it remains highly probable that at least some portion of MPs found in Southern Ocean Sea ice arise from atmospheric contributions. Backwards, air mass trajectories from the first study of MPs in Antarctic snow indicated that MPs entering the Southern Ocean likely arrive via long-range transport, most notably from South America, upwards of 6,000 km away from their sampling sites in the Ross Sea region, though local sources from Scott Base and McMurdo Station contributed as well^[16]. Similarly, air mass trajectories conducted for a cruise from East Asia to Antarctica indicate that MPs likely originated from the continents of South Asia and Oceania^[61], with non-fibrous MP concentrations decreasing with increasing latitude. Finally, the ocean-atmosphere exchange of MPs may also contribute locally to our sea ice concentrations^[75]. Particles - particularly in coastal surface waters - can be re-entrained in the atmosphere via sea mist^[75]. With these combined conclusions, it may be that long-range transport facilitates MP contamination across the STF, where a portion of airborne MPs become incorporated into surface waters for inclusion into growing ice. An additional portion of MP particles that remain or become airborne could integrate into sea ice via snow deposition. Cunningham et al. (2022) found MP types consistent in air masses and seawater, and thus, they similarly speculate that atmospheric and oceanic processes influence Antarctic MP presence in tandem^[18].

It is difficult to pinpoint specific sources of MP contamination. However, the MP fragments found in our samples are typically abundant in the marine environment and have several uses in and out of a marine context. PP, PE, PUR, PVC, PET, and PS are the most abundant marine MPs, comprising approximately 80% of total plastic production^[76], and all six polymers were found in high abundance in our study, totaling 78.9% of all MPs identified [Table 2]. The most abundant polymer types were PP and PE and were present in all 19 ice cores. This coincides with PP and PE being the most abundant marine MPs globally and around the Southern Ocean^[7,66,72], and aligns with global production rates^[77,78]. PP and PE are commonly associated with maritime and fishing activities and land-based beach litter, and this, combined with their low density, makes them readily abundant in surface waters^[79]. Additionally, PP was the most abundant polymer found in atmospheric deposition samples inland of the Ross Sea region (coastal Victoria Land), and was linked to potential human activities at nearby research stations^[80]. PET accounted for 49% of polymers found in a study of Antarctic snow, with the authors suggesting that both local and distant sources could be contributing to this phenomenon^[16]. PET and PA are commonly used in textiles and have high correlations with wastewater^[81,82]; thus, while all polymers could penetrate the Southern Ocean via long-range transport, there is potential that these polymers originate from local Antarctic stations or - what is more likely - vessels. Interestingly, PAN and PVC were also found in relatively high quantities across our samples, ranked in the top three for marine polymers of concern^[83]. Despite their densities being higher than that of seawater, they have been found in other Southern Ocean samples^[7,84]. For cores collected over shallower water depths, we suspect that plastic-laden marine sediments may be resuspended during storms or other turbulent conditions, allowing for the incorporation of these denser MPs into sea ice. Compositionally, PAN was the third most prevalent polymer in fast ice, accounting for over 22% of all MPs, compared to just 6% for pack ice. Ultimately, the high variability in abundance and polymeric composition across our samples makes it difficult to draw conclusions regarding the immediate sources of this debris.