## 4 Research Focus and Trend  
A range of most frequent keywords and co-words were computed using Biblioshiny (Table 2). Co-words are pair of key terms that co-occur within a paper and the analysis was undertaken based on the frequency of co-occurrence. This approach enables researchers to postulate the knowledge structure and significant topics in the current research field. In this study, top-ranked keywords from both categories showed a degree of similarity. The exam \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Date** & **Vessel/Station** & **Location** & **Incident and Environmental Impact** & **Reference** \\ \hline
18 January 1997 & _Akudemit Sergei_ & Howgaard, Antarctic & Estimated 4 L of oil and lubricant leaked & \\  & _Vavilov_ & Peninsula & from rubber casing resulted from event in & [16] \\  & & & open sea. & \\ \hline
28 December 2001 & _Vista Mar_ & Hope Bay, Antarctic & Propeller damaged during manoeuvring & [17] \\  & & Peninsula & resulted in gland oil leakage (<1 L). & \\ \hline
23 November 2007 & _Explorer_ & Drake Passage & Vessel sunk after striking ice. 210,000 L of oil, petroleum and lubricants spilled. & [18] \\ \hline
26 December 2009 & _Clelia II_ & Petermann Island & Propeller damaged after striking rocks. & \\  & & & Trace amounts of lubricants leaked from & [16] \\  & & & drive shaft. & \\ \hline
16 March 2011 & _Oliva_ & Nightingalelsland, Tristan da Cunha & Vessel sunk offshore of rock-hopper & \\  & & & penguin colonies (International Union for & \\  & & & Conservation of Nature, IUCN & \\  & & Group & Endangered species). Approximately 1500 & \\  & & & tonnes bunker fuel spilled resulted in & \\  & & & widespread oiling of marine vertebrate. & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: \(Cont.\)  
Figure 1: Scientific publications from 1980 to 2019 grouped into four decades. ples were hydrocarbon, polycyclic aromatic hydrocarbon (PAH), toxicity, biodegradation, bioremediation and bacteria. Diesel hydrocarbon composition is one of the study focus as winter diesel is treated apart from normal fuel refinery. High molecular weight paraffins with limited solubility are prone to wax crystal precipitation when the fuel cools down. To prevent gelling of diesel in cold temperature, high molecular weight paraffins are selectively reduced in diesel to lower its density and viscosity [20]. Due to different origin of crude, refinery and post-processing treatment, commonly used winter diesels such as Special Antarctic Blend diesel (SAB), marine gas oil (MGO) and intermediate grade of fuel oil 180 (IFO 180) contain varying hydrocarbon compositions formulated for use in the Antarctic conditions. SAB is the most used fuel at the Antarctic and sub-Antarctic regions (i.e., Australian Antarctic research stations) with an annual consumption of 2 million litres [21]. It is a middle distillate containing 96% volatile compounds, primarily alkanes in the range \(n\)-C\({}_{9-14}\) and other branched alkanes, cycloalkanes as well as aromatic hydrocarbons. Both SAB and MGO are similar in density and viscosity, but MGO is composed of \(n\)-C\({}_{9-25}\) range of alkanes. IFO 180 is a heavier complex mixture of mainly residual oil and middle distillate constituting 6% to 7% of the fuel. The composition of an IFO 180 includes a wide carbon range of C\({}_{6}\) to \(>\)\(n\)-C\({}_{40}\) and may contain PAHs from cracked components, hence is the densest [22]. Diesel toxicity is another hot topic that is usually addressed with hydrocarbon composition. Certain proportions of the hydrocarbon compounds are able to produce a water-accommodated fraction (WAF) when in contact with water [23]. The bioavailability of WAF towards marine organisms is attributed to the ecological impacts of oil spillage.